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. 2022 Nov 18;33(14):br25. doi: 10.1091/mbc.E22-07-0297

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FIGURE 3: — Bivalents with monooriented long arms exhibit defects in chromosome migration on the spindle. (A) Wild-type (EU1067), him-18(tm2181) and akir-1(rj1) Meiosis I spindles arrested in metaphase via emb-30(RNAi); shown are DNA (blue), tubulin (green), and AIR-2 (red). Chromosome alignment was calculated by measuring the distance between the two most poleward rings (R) and then dividing that distance by the pole-to-pole length of the spindle (S). There are defects in bivalent alignment in him-18(tm2181) spindles compared with wild-type (p value = 4.73 × 10^–7; two-tailed Student’s t test), but no significant defects in akir-1(rj1) mutants (p = 0.09). Additionally, the distance between each RC and its nearest pole was measured (Q) and divided by spindle length (S) to assess individual chromosomes; a value of 0.5 means a chromosome is at the center of the spindle, whereas a smaller value denotes a chromosome located closer to a pole. Note that some values are above 0.5 since the measurements were made on 3D renderings of each spindle; if a chromosome was found above or below the pole-to-pole spindle axis, the distance was measured at an angle, sometimes resulting in a measurement greater than half of the pole-to-pole distance. There are defects in bivalent alignment in him-18(tm2181) spindles compared with wild-type (p value = 3.80 × 10^–13; two-tailed Student’s t test), but no significant defects in akir-1(rj1) mutants (p = 0.76). (B) Meiosis I him-18(tm2181) spindles arrested in metaphase via emb-30(RNAi); shown are DNA (blue), tubulin (green), and SUMO (red). Single-slice zooms show examples of “stacked” bivalents (zoom 1; left), where the bivalent lobes are pointed to opposite spindle poles, and “cracked” bivalents (zoom 2; right), where the bivalent is monooriented with the RC toward one spindle pole and both bivalent lobes toward the other. (C) Wild-type (EU1067), him-18(tm2181) and akir-1(rj1) monopolar spindles generated by klp-18(RNAi); shown are DNA (blue), tubulin (green, column 1), SUMO (green, column 2), and ASPM-1 (red). Chromosome migration distances were measured from the center point of the ASPM-1 volume to the poleward face of each bivalent. Migration of stacked him-18 bivalents was not significantly different from wild-type bivalents (p = 0.78; two-tailed Student’s t test), while him-18 cracked bivalents did not migrate as far (p < 8.66 × 10^–23). akir-1(rj1) bivalents had a small but significant migration defect compared with wild-type (p = 0.0001). Scale bars = 5 µm (full images), 1 µm (zooms).