Fig. 8.

Spindle migration following anaphase-onset delays furrowing. a Schematic for defining orientation of cortex-proximal spindles relative to cortex. Spindles were considered non-perpendicular if θ > 10°. b Spindle orientation at anaphase-onset. Error bars are mean ± SEM. Oocyte numbers are shown in parentheses from a minimum of three independent experiments. c–f Untreated oocytes, which at the time of anaphase-onset, have spindles located either at the cortex (c, d, f) or at the oocyte-centre (e) and oriented either perpendicular (c) or non-perpendicular (d, f). Typically, asymmetry results after perpendicular spindles migrate into the membrane following anaphase-onset leading to displacement of around half of the spindle beyond the oocyte (c; see Supplementary Movie 30). Near-symmetrical cleavage if cortically located non-perpendicular spindles do not induce migration/protrusion (d; see Supplementary Movie 31). Furrowing (arrowhead) occurs at the midzone-proximal membrane (*) but not at the distal membrane (#) for cortically located spindles (d) and is two-sided in the case of central spindles (arrowheads, e; see Supplementary Movie 32). Migration/protrusion enables cortically located non-perpendicular spindles to produce extreme asymmetry (f; see Supplementary Movie 33). g, h Model of anaphase-spindle migration/protrusion that positions half of the spindle external to the oocyte (g) and comparison with symmetry and asymmetry models in which the anaphase spindle remains internal to the mother cell (h). Times in panels are hours:minutes relative to anaphase-onset. Scale bars, 10 µm