Fig. 2

A rpr-triggered caspase cascade dismantles the cortical F-actin cytoskeleton in living salivary glands. a Maximal intensity projection of a whole salivary gland at −8 h PF expressing the actin-binding peptide Lifeact-Ruby in red and the membrane marker CD8-GFP in green, both under control of the salivary gland driver fkh-GAL4. CD8-GFP is enriched at the apical membrane (proximity of Lifeact-Ruby and CD8-GFP at the apical membrane appears yellow); nuclei stained by DAPI in blue. b, c Confocal slices through the salivary glands. b A medial slice shows an apical–basal view of acinar cells, with the lumen in the middle. c A lateral slice shows a “coronal” view, highlighting the cortical F-actin cytoskeleton. d, e Cortical F-actin breaks down at the end of larval development. d Phalloidin staining (white) in salivary glands at −8 h PF reveals tight cortical bundles of F-actin; this structure begins to disintegrate at −4 h PF and −1 h PF, with no phalloidin staining visible by 0 h PF. e Lifeact-Ruby in salivary glands confirms cortical F-actin breakdown. Lifeact-Ruby reveals that most of the actin in the cell is present at the cortex at −8 h PF. Breakdown of F-actin is reflected by a gradual redistribution of Lifeact-Ruby signal from the cortex to the cytoplasm at −4 h PF and −1 h PF, with only cytoplasmic signal visible at 0 h PF. f F-actin dismantling requires caspase activity. F-actin breakdown is blocked in rpr, dronc, and dcp-1 mutant salivary glands, but not in drice mutant salivary glands. g Caspases regulate F-actin breakdown cell-autonomously. Salivary gland-specific (using Sgs3-GAL4) overexpression of rpr-RNAi, dronc-RNAi, or of the caspase inhibitors diap1 or p35 inhibits F-actin breakdown. Scale bars represent 100 µm. Df, deficiency, PF, puparium formation