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Fig. 5. Microtubule distribution and furrow induction in cut cells containing a half-spindle and segregated chromosomes. Spermatocytes (A, 0 minutes) were cut in two (8 minutes) between segregating chromosomes in early anaphase, exposing plus-ends of overlapping microtubules (Ba, green). As chromosomes continue to move poleward (8-40 minutes; see also Movie 5, http://jcs.biologists.org/supplemental/), both mitochondria (0-8 minutes, m) and actin filaments (f, red), slightly disorganized by cutting, are excluded toward microtubule plus-ends at the cell periphery (15-25 minutes; f,g, red). When chromosomes arrive at the pole (40 minutes), a new half-spindle emerges and overlaps with cut plus-ends of original half-spindle microtubules (c, green), forming an extremely asymmetric `midzone' (c, arrows). Actin filaments (h, red) continue to follow microtubule plus-ends, now overlapping at the midzone, whereas mitochondria begin to extend along microtubules (40 minutes onwards). Furrow initiation (68-83 minutes, arrows) and contractile ring formation (i, red) occur at the asymmetric midzone, displaced 48.6±3.8% (n=8) away from the central position. As the furrow ingresses, the contractile ring (i,j, red) and furrow (83 minutes onward) follow the midzone position (c-e, arrows), becoming progressively more symmetric with respect to the central spindle because of elongation of the new half-spindle (c-e, green). But the furrow remains asymmetric to the cell because of the initial asymmetry at furrow initiation (140 minutes). Scale bars: 10 µm.
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