Figure 4.
Turnover of MyoII and F-actin affects medioapical contractile dynamics and is essential for tissue integrity. (A) Regulation of actomyosin contractility. (B–D) Apical cell outlines labeled with α-Cat::GFP in (B) WT, (C) MLCKCA, and (D) DiaCA-expressing eyes. Green and purple overlays highlight LCs and 1° cells, respectively. (C) MLCKCA expression results in clustering of LCs around mechanosensory bristles (yellow arrows). The AJs appear fragmented, cells rupture (asterisks), and the planar polarization of ommatidia is disrupted. (D) DiaCA expression also results in clustering of LCs (yellow arrow), fragmentation of AJs, and cavitation of cone cells (white arrow). (E) MLCKCA expression significantly decreases the apical cell area of 2° LCs, while DiaCA expression increases apical cell area compared with WT. One-way ANOVA with Dunnett’s multiple comparisons. WT versus MLCKCA mean R-difference of 3.042, P < 0.0001. WT versus DiaCA, mean R-difference of −3.352, P < 0.0001, N = 20 for WT, 15, and 14, respectively, from three eyes each. (F) MLCKCA expression leads to cell rupture. Snapshot from a time-lapse movie (Video 5) of F-actin (Utr::GFP) and MyoII (Sqh::mCh) showing a ruptured cell (marked by the dotted circle) and filamentous actin (green arrowhead) connecting MyoII foci (orange arrowheads) across the rupture. (F′) MyoII dynamics in a MLCKCA-expressing eye. A medioapical MyoII ring repeatedly expands (green arrows) and contracts (red arrow). (F″) In MLCKCA the frequency of medioapical MyoII ring pulsing is ∼10 min ± 2.5 min (N = 10, 30 pulses in three eyes). (F‴) Medioapical MyoII levels are negatively correlated with the apical area of 2° LCs (R = −0.2126, one-sample t test, P = 0.0044, N = 15 in three eyes). (G) In DiaCA-expressing eyes, F-actin forms a wide band at the cell periphery and dynamic medioapical F-actin is not present (representative LC from four time-lapse movies). Scale bar = 3 µm.

Turnover of MyoII and F-actin affects medioapical contractile dynamics and is essential for tissue integrity. (A) Regulation of actomyosin contractility. (B–D) Apical cell outlines labeled with α-Cat::GFP in (B) WT, (C) MLCKCA, and (D) DiaCA-expressing eyes. Green and purple overlays highlight LCs and 1° cells, respectively. (C) MLCKCA expression results in clustering of LCs around mechanosensory bristles (yellow arrows). The AJs appear fragmented, cells rupture (asterisks), and the planar polarization of ommatidia is disrupted. (D) DiaCA expression also results in clustering of LCs (yellow arrow), fragmentation of AJs, and cavitation of cone cells (white arrow). (E) MLCKCA expression significantly decreases the apical cell area of 2° LCs, while DiaCA expression increases apical cell area compared with WT. One-way ANOVA with Dunnett’s multiple comparisons. WT versus MLCKCA mean R-difference of 3.042, P < 0.0001. WT versus DiaCA, mean R-difference of −3.352, P < 0.0001, N = 20 for WT, 15, and 14, respectively, from three eyes each. (F) MLCKCA expression leads to cell rupture. Snapshot from a time-lapse movie (Video 5) of F-actin (Utr::GFP) and MyoII (Sqh::mCh) showing a ruptured cell (marked by the dotted circle) and filamentous actin (green arrowhead) connecting MyoII foci (orange arrowheads) across the rupture. (F′) MyoII dynamics in a MLCKCA-expressing eye. A medioapical MyoII ring repeatedly expands (green arrows) and contracts (red arrow). (F″) In MLCKCA the frequency of medioapical MyoII ring pulsing is ∼10 min ± 2.5 min (N = 10, 30 pulses in three eyes). (F‴) Medioapical MyoII levels are negatively correlated with the apical area of 2° LCs (R = −0.2126, one-sample t test, P = 0.0044, N = 15 in three eyes). (G) In DiaCA-expressing eyes, F-actin forms a wide band at the cell periphery and dynamic medioapical F-actin is not present (representative LC from four time-lapse movies). Scale bar = 3 µm.

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