Shroom is required for convergent extension and multicellular rosette formation. (A and B) Stills of time-lapse videos of wild-type (WT; A) and Shrm^Δ11 mutant (B) embryos expressing Spider:GFP (t = 0 is the onset of elongation in early stage 7). Stage 7 (0–10 min); stage 8 (10–30 min). Anterior is left, and ventral is down. Rosettes (groups of five or more cells that meet at a vertex) are highlighted. Bar, 10 µm. (C–F) Cell behavior in wild-type (blue) and Shrm^Δ11 mutant (red) embryos. (C) Tissue aspect ratio (tissue length along the AP axis relative to its width along the DV axis) normalized to the value at t = 0. Shroom mutants have a reduced tissue aspect ratio in stage 8 (P = 0.02 at 30 min). (D and E) Neighbors lost per cell through neighbor exchange, also known as a T1 process (resulting from single edge contraction events; D) and rosette formation (resulting from the contraction of multiple, consecutive edges; E). Rosette formation was significantly reduced in Shroom mutants (P < 0.001 at 30 min). Local neighbor exchange was not significantly affected (P = 0.63 at 30 min). (F) Mean number of neighbors per cell. Wild-type cells have progressively fewer neighbors midway through elongation as a result of cell rearrangement. Cells in Shroom mutants have more neighbors on average midway through elongation (P < 0.001 at 20 min), consistent with reduced cell rearrangement. Videos of four wild-type Spider:GFP and eight Shroom mutants were analyzed at 15-s intervals (185–276 cells tracked/embryo). Means ± SEM between embryos are shown.