Fig. 3. Microtubule distribution and furrow induction in cells containing a bipolar spindle and the X chromosome. Following removal of all bivalents, microtubule density increases at the pole bearing the X chromosome, which is shown in both polarization microscope images (A, 0-57 minutes; see also Movie 2, http://jcs.biologists.org/supplemental/) and a cell fixed at the corresponding stage and stained (B) for microtubules (a, green), actin filaments (e, red), and the chromosome (a, blue). The asymmetric microtubule distribution shifts mitochondria (m) away from the chromosome bearing pole (0-57 minutes). Anaphase onset is recognized as a spilt of the X chromosome (82 minutes, circle in A) arms (b, blue) and disassembly of spindle microtubules, which appears as a reduction in spindle birefringence (82-104 minutes) and fluorescence (a,b, green). During anaphase (87 minutes) mitochondria (arrowheads) and actin filaments (f, red) accumulate at the midzone (82-87 minutes; b, arrows), which is shifted away from the pole with greater microtubule density. Following anaphase, mitochondria extend along microtubules (87-122 minutes) as actin filaments bundle into the contractile ring (f,g, red; see also Movie 3, http://jcs.biologists.org/supplemental/) around the shifted midzone (c, arrows), asymmetrically inducing cell cleavage 16±2% from the genuine central position of the spindle (104 minutes, arrows; n=7). Despite spindle reorganization (c,d, arrows) that symmetrically shifts the midzone and furrow (104 minutes onward; g,h, red) along the central spindle, the initial asymmetry to the cell remains (152 minutes; d,h). Scale bars: 10 µm.