Fig. 4. SPD-1 depletion fails to abolish spindle-side furrowing, and makes far-side furrowing both deeper and more persistent. (A) Time-lapse sequence of the mitotic apparatus in a SPD-1-depleted zygote. The mitotic apparatus appears completely normal in metaphase (frame 1). When spindle poles move apart in anaphase, however, no microtubules remain between the separated chromosomes (frames 2 and 3). Kinetochore fibers break down, spindle poles swell, and furrowing initiates, as in wild-type embryos (frames 4 and 5). The only trace of the midzone microtubule array is a slender bundle of astral microtubules constricted by the cytokinetic furrow (frame 6, arrowhead). (B) Perforated SPD-1-depleted zygote. Asterisks in frame 1 mark the approximate position of spindle poles. The cortex around the probe recruits myosin uniformly instead of only on the side apposed to the spindle (frames 2-4). Furrows initiate both on the far side and spindle side of the perforation (frame 3, arrowheads). Both furrows ingress to completion (frames 4-6). (C) Perforated SPD-1-depleted AB. Asterisks mark approximate positions of spindle poles. Myosin recruitment takes place on the spindle side equatorial cortex, along the spindle side of the probe, and on the far side equatorial cortex (bracket in frame 2). Both far side and spindle side develop ingressions (frame 3; arrowhead in frames 3-5 marks the far-side furrow); at the time the spindle-side furrow completes (frame 4) the far side maintains a myosin-enriched furrow which ingresses deeply (frame 5), but ultimately regresses (frame 6). Bar, 10 µm; ss, spindle side; fs, far side from the perforation.