Figure 2.
The medioapical actomyosin network holds tension and mechanically links neighboring LCs. (A) High-resolution Airyscan images of F-actin and MyoII from a time-lapse movie (representative ommatidia from six Airyscan movies). The 2° and 3° LCs are highlighted by the green and blue overlays, respectively. Left: Medioapical actomyosin nodes (yellow arrowheads) that form a ring structure are connected to nodes at the cell surface (orange arrowheads) via filamentous structures (blue arrowhead). Right: Medioapical actomyosin nodes form a ring structure (red arrowheads) that links to nodes at the cell surface (orange arrowheads). (B–E) Targeted ablations (Video 2) of medioapical actomyosin in LCs (marked with a yellow star) induce a rapid recoil of medioapical actomyosin and lead to apical cell area expansion. (B) Medioapical actomyosin ablation in 2° LCs induces preferential expansion of the LC–LC contact and actomyosin flow (tracked by the ellipse) toward LC–LC contacts (white arrowheads) concomitant with apical area relaxation (green overlay highlights the 2° LCs, green double arrows point to the direction of cell expansion). Top: Snapshots of a lattice edge from a time-lapse movie; Bottom: Zoomed-in views of F-actin and MyoII (N = 10 cells from three eyes). (C) Ablations in which only some medioapical actomyosin recoiled exhibit weaker apical area expansion (green overlay highlights the 2° LCs) (N = 3 partial ablations of 27 ablations). White arrowheads mark contacts with neighboring cells in the lattice. (D) Ablation of the medioapical actomyosin network in 3° LCs (highlighted by a blue overlay) induces a strong relaxation of the apical cell area and a preferential expansion of 3°-1° contacts compared with LC–LC (3°-2°) contacts (N = 10 cells from four eyes). White arrowheads point to LC–LC contacts. Green double arrows point to the direction of cell expansion. (E) Left panel: Fold change of the 2° LC area and cell–cell contacts after ablation. Two-way ANOVA was performed with Sídák’s multicomparison to compare each data set before to after ablation. 2° LCs area after ablation versus before ablation, P < 0.0001, N = 10. 2°-3° contact length after ablation versus before ablation, P < 0.0001, N = 10. 2°-1° contact length after ablation versus before ablation, P = 0.1569, N = 10 from four eyes. Right panel: Fold change of the 3° cell area and cell–cell contact before and after ablation. 3° LCs area after ablation versus before ablation, P < 0.0001, N = 8 from four eyes. 3°-2° contact length after ablation versus before ablation, P = 0.0015, N = 8 from four eyes. 3°-1° contact length after ablation versus before ablation, P < 0.0001, N = 8 from four eyes. (F) A cartoon depicting the forces affecting cell shape inferred from the pattern of recoil of 2° and 3° LCs after ablation. Red arrows depict contractile forces, and their thickness represents their magnitude. Green arrows depict the passive stretching of the 2°-1° cell contacts in response to the contraction of the 3° LCs. (G) Left: Snapshots from a time-lapse movie of a lattice edge before and after 2° LC ablation. In the MyoII channel, the ablated 2° cell is highlighted in green and the adjacent non-ablated 3° LC in blue. After ablation (marked with a yellow star), the apical area of the neighboring 3° LC initially expands (green arrow). This is followed by an increase in medioapical actomyosin (red arrow) and cell area contraction. (G′) Approximately half of the non-ablated neighboring LCs (14 cells out of 27 cells in nine eyes) assembled a robust medioapical actomyosin network and contracted after ablation of their neighboring cell. Scale bar = 3 µm.

The medioapical actomyosin network holds tension and mechanically links neighboring LCs. (A) High-resolution Airyscan images of F-actin and MyoII from a time-lapse movie (representative ommatidia from six Airyscan movies). The 2° and 3° LCs are highlighted by the green and blue overlays, respectively. Left: Medioapical actomyosin nodes (yellow arrowheads) that form a ring structure are connected to nodes at the cell surface (orange arrowheads) via filamentous structures (blue arrowhead). Right: Medioapical actomyosin nodes form a ring structure (red arrowheads) that links to nodes at the cell surface (orange arrowheads). (B–E) Targeted ablations (Video 2) of medioapical actomyosin in LCs (marked with a yellow star) induce a rapid recoil of medioapical actomyosin and lead to apical cell area expansion. (B) Medioapical actomyosin ablation in 2° LCs induces preferential expansion of the LC–LC contact and actomyosin flow (tracked by the ellipse) toward LC–LC contacts (white arrowheads) concomitant with apical area relaxation (green overlay highlights the 2° LCs, green double arrows point to the direction of cell expansion). Top: Snapshots of a lattice edge from a time-lapse movie; Bottom: Zoomed-in views of F-actin and MyoII (N = 10 cells from three eyes). (C) Ablations in which only some medioapical actomyosin recoiled exhibit weaker apical area expansion (green overlay highlights the 2° LCs) (N = 3 partial ablations of 27 ablations). White arrowheads mark contacts with neighboring cells in the lattice. (D) Ablation of the medioapical actomyosin network in 3° LCs (highlighted by a blue overlay) induces a strong relaxation of the apical cell area and a preferential expansion of 3°-1° contacts compared with LC–LC (3°-2°) contacts (N = 10 cells from four eyes). White arrowheads point to LC–LC contacts. Green double arrows point to the direction of cell expansion. (E) Left panel: Fold change of the 2° LC area and cell–cell contacts after ablation. Two-way ANOVA was performed with Sídák’s multicomparison to compare each data set before to after ablation. 2° LCs area after ablation versus before ablation, P < 0.0001, N = 10. 2°-3° contact length after ablation versus before ablation, P < 0.0001, N = 10. 2°-1° contact length after ablation versus before ablation, P = 0.1569, N = 10 from four eyes. Right panel: Fold change of the 3° cell area and cell–cell contact before and after ablation. 3° LCs area after ablation versus before ablation, P < 0.0001, N = 8 from four eyes. 3°-2° contact length after ablation versus before ablation, P = 0.0015, N = 8 from four eyes. 3°-1° contact length after ablation versus before ablation, P < 0.0001, N = 8 from four eyes. (F) A cartoon depicting the forces affecting cell shape inferred from the pattern of recoil of 2° and 3° LCs after ablation. Red arrows depict contractile forces, and their thickness represents their magnitude. Green arrows depict the passive stretching of the 2°-1° cell contacts in response to the contraction of the 3° LCs. (G) Left: Snapshots from a time-lapse movie of a lattice edge before and after 2° LC ablation. In the MyoII channel, the ablated 2° cell is highlighted in green and the adjacent non-ablated 3° LC in blue. After ablation (marked with a yellow star), the apical area of the neighboring 3° LC initially expands (green arrow). This is followed by an increase in medioapical actomyosin (red arrow) and cell area contraction. (G′) Approximately half of the non-ablated neighboring LCs (14 cells out of 27 cells in nine eyes) assembled a robust medioapical actomyosin network and contracted after ablation of their neighboring cell. Scale bar = 3 µm.

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