Fig. 4. Microtubule distribution and furrow induction in cells containing a monopolar spindle and the X chromosome. Following removal of all bivalents and one aster, the spindle becomes monopolar as microtubules are stabilized around the X chromosome and the remaining pole (A, 0 minutes; see also Movie 4, http://jcs.biologists.org/supplemental/; Ba, green). Mitochondria, scattered at the spindle periphery initially, accumulate at the plus-ends of radiating spindle microtubules (0-32 minutes, arrowheads; a, green). Following anaphase, as recognized by the separation of the X chromosome (50 minutes, arrow), mitochondria move back toward the original pole along central spindle microtubules (50-87 minutes). Accumulation of actin filaments (f, red) and furrow initiation are shifted 42±2.1% (87 minutes, arrows; n=5) from the central position to the `midzone' (b, arrows), asymmetrically defined by microtubules from the original and newly established half-spindles. The furrow ingresses (87 minutes onward) as actin filaments accumulate and constrict (g,h, red) the midzone (c,d, arrows). Owing to microtubule elongation at the new half-spindle (c,d, green), the furrow eventually becomes more symmetric with respect to the central spindle (142 minutes) but retains its asymmetry with respect to the cell (97 minutes onwards). Scale bars: 10 µm.