Fig. 1. Chromosome alignment and spindles during meiotic division in wild-type (WT) and G₄ TR^–/– (TRKO) mouse oocytes. (A) MI stage at 9 h of culture, showing misalignment of chromosomes (red) on spindles (green) in TR^–/– mouse oocytes. (B) AI–TI stage, showing complete separation of chromosomes in wild-type mouse oocytes but chromosome scattering in TR^–/– mouse oocytes. (C) MII stage at 12–14 h of culture, showing misalignment (arrows) of chromosome over disrupted spindles in TR^–/– mouse oocytes, in contrast to equatorial chromosome alignment over the bipolar barrel-shaped spindles of wild-type mouse oocytes. Arrowheads indicate the first polar body. Scale bars (A–C), 10 µm. (D) Higher magnification of (C), showing that aligned chromosomes appeared to attach to microtubules, whereas misaligned chromosomes were not attached but with free ends (arrows). Scale bar, 4 µm.