Myosin contractility suppresses Sna-dependent junction disassembly. (A) Strong myosin RNAi (sqh RNAi) leads to junction loss only in mesodermal cells (ventral) but not in ectodermal cells (dorsal and lateral). Bar, 20 µm. (A′–A′″) Enlarged images of ventral, lateral and dorsal cells, respectively. Bar, 10 µm. (B) Junctions stained by Arm in control embryos with GFP expression. (C) Misexpression of Sna in the whole embryo causes junction loss in ectodermal cells, whereas junctions in apically constricting ventral cells remain. (D) Myosin activation in the whole embryo restores junctions in the presence of Sna misexpression. (C′ and D′) Sna staining in the same embryos as C and D. Bar, 20 µm. β-Cat, β-catenin.