Fig. 2. During mitosis two autonomous spindles are responsible for chromosome segregation after nuclei migrate to the cell center. The centromere-specific histone cenH3 marks centromeres (cenH3:GFP in green, A-C,G-I), and centrin antibodies mark spindle poles (green, D-F,J-L). TAT1 (anti-tubulin) labels the microtubule cytoskeleton including the mitotic spindles (all cells, in red) and DAPI labels chromatin (all cells, in blue). Behavior of left (red) and right (blue) nuclei is diagramed above each stage. (A) Interphase; centromeres are discreet foci in each nucleus. (D) Interphase; centrin stains two foci in association with the flagellar basal bodies between the two nuclei. (B) Prophase; spindle microtubules appear between the two nuclei and extend around each nucleus. Centromeres are one spot on each condensed chromosome. (E) Prophase; four centrin foci are associated with the forming spindles. (C) Metaphase; following nuclear migration the nuclei become stacked along the dorsal-ventral axis. The microtubules organized into two bipolar spindles. (F) Metaphase; centrin foci are at the four spindle poles. (G) Anaphase; chromatin is segregated to spindle poles along the left-right axis of the cell with centromeres clustered at the spindle poles. (J) Anaphase; centrin remains at the spindle poles. (H) Telophase; a linear microtubule structure replaces the bipolar spindles and centromeres remain clustered. (K) Telophase; centrin foci are between the two nuclei of each daughter. (I) Cytokinesis; chromatin decondenses and the cleavage furrow forms at the anterior end, creating a heart-shaped cell. (L) Cytokinesis; centrin stains two foci between the nuclei. Cytokinesis divides the cell into left and right halves. Bar, 2 µm.