F-actin is required for maintaining membrane integrity during furrow invagination. (A) In untreated cycle-12 embryos, membrane (GFP-Dlg, green) is closely surrounded by F-actin (red) at the furrow. (B) 2 mM LatA or DMSO was injected at cycle-13 early prophase. GFP-Dlg–marked plasma membrane was progressively lost (arrowheads) as furrows invaginated in LatA-injected embryos (top row). Membrane loss started after most of the F-actin was lost at the furrow (middle row). (C) Furrow integrity was monitored relative to spindle spacing and dynamics (tubulin, red). Spindle fusion (asterisks) occurred where membrane (Dlg, green) was lost at the furrow. See Video 2 . Bars, 10 μm.