Fig. 3. Microfilaments bundle ectopically in cortex following BDM treatment. Xenopus zygotes were exposed to 20 mmol/l BDM beginning at 0.38 NT (A) or 0.94 NT (B) after fertilization. The earlier BDM exposure caused extensive contraction and irregular blebbing in the animal cap (A). Rhodamine-phalloidin staining of the surface, showing long, branching ectopic microfilament bundles (A'). The later BDM exposure induced torsion between the two cleaving blastomeres (offset indicated by paired arrowheads in B) and extensive bundling of ectopic actin fibers that branched and spread across cortex from the growing edge of the contractile ring (arrows in B'). Scale bars: 10 µm in A'; 75 µm in B.