Fig. 3. Perforated cells consistently recruit myosin II to the far-side equatorial cortex. (A) Frames from a time-lapse sequence of a perforated zygote. In frame 1 asterisks indicate the approximate position of the spindle poles, inferred from the cloud of GFP-myosin that appears on the metaphase spindle. In both unmanipulated and perforated zygotes, the first phase of cytokinetic myosin recruitment is an array of blotches (frame 2), which appear broadly on the cell surface, then rapidly resolve into an equatorial band. Brackets in frame 3 mark the extent of the equatorial myosin zone on both the spindle side and far side. Often, as in this case, the far-side myosin zone is noticeably fainter than the spindle-side zone (although see Fig. 5B). Nevertheless this weak zone coincides with a shallow, persistent furrow (this embryo was scored for two furrows in Fig. 2A). The cortex around the probe recruits myosin intensely on the side facing the spindle. (B) Frames from a time-lapse sequence of a perforated AB. Frame 1 is before nuclear envelope breakdown; myosin is present everywhere on the cortex in AB, but not P1, before anaphase. Asterisks in frame 2 mark the approximate positions of spindle poles. During anaphase, myosin disappears from the polar cortex, but remains and brightens on both the spindle-side and far-side equatorial cortex (frame 3). The cortex between the probe and the spindle also develops an intense myosin zone (frame 4; brackets indicate the approximate extent of equatorial myosin zones) and, although myosin persists on the far side cortex, in this case furrowing occurs only on the spindle side (frame 5; this embryo was scored for one furrow in Fig. 2B). Shortly after nuclei reappear (dark spots, frame 6) myosin can no longer be detected on the far-side cortex. Bar, 10 µm; ss, spindle side; fs, far side from the perforation.