The tricellular vertex-specific adhesion molecule Sidekick facilitates polarised cell intercalation during Drosophila axis extension
Fig 5
Apical adhesion is disrupted during polarised cell intercalation in sdk mutants.
(A) A single z-frame at the level of AJs showing a gap or tear in the cortex at a presumed rosette centre in an sdk mutant embryo. Left panel shows merge between DE-Cad-GFP and Sqh-mCherry (shortened as MyoII-mCherry) signals, right panel, DE-Cad-GFP channel only. In the bottom panel, the different cells have been coloured to highlight the apical gap in the middle. (B) Single z-frames at different positions along the apicobasal axis of an apical gap in an sdk mutant embryo (from movie shown in S6A Fig) at the level of AJs (0 μm) and 1 and 2 μm below. The gap present at the level of AJs is closed in the planes basal to the AJs. Bottom panels show colourised cells, highlighting the apical gap in the apical-most z-slice. (C) Fixed and stained sdk mutant embryo against DE-Cad and GFP (to reveal MyoII-GFP), imaged by SIM super-resolution microscopy at stage 7. Each image is a maximum intensity projection over 3 μm at the level of AJs in the ventral ectoderm. Regions bounded by yellow and blue lines show discontinuities in E-Cad signal, indicating holes in apical adhesion, and are shown below as close-ups. (D–F) Apical gaps quantifications in WT and sdk mutant movies as shown in A, B. (D) Quantification of the number of gaps found at the level of AJs, normalised to a given area (2,500 μm2) of the ectoderm. One to two regions (embryo sides) were quantified per movie: WT, n = 7, from seven embryos; sdk mutant n = 10, from eight embryos; Mann–Whitney, p-value = 0.0018. (E) Quantification of how long apical gaps persist in the tissue. (F) Quantification of how long apical gaps persist as a function of the number of cells present at the gap’s border. We detected gaps where four to seven cells and more meet. For both E and F, the number of gaps quantified was n = 92 for WT and n = 115 for sdk mutant. In D, Mann–Whitney, p-value < 0.0001. Data for graphs D–F can be found at https://doi.org/10.17863/CAM.44798. AJ, adherens junction; DE-Cad, DE-Cadherin; GFP, green fluorescent protein; MyoII, Myosin II; Sdk, Sidekick; SIM, Structured Illumination Microscopy; Sqh, spaghetti-squash; WT, wild type.