Fig. 3: Mitotic spindles display dynamic structural changes during medaka early cleavage.

a Representative live-cell images showing metaphase spindles in indicated embryonic stages. Solid and dashed lines indicate the centrosome-centrosome distance and the cell diameter, respectively. b Left: Fluorescence intensity on the yellow line was measured. Right: Graphs of fluorescence intensities for line scans of spindles in (a) showing an increase of EGFP-α-tubulin intensity at the spindle midplane in 2-cell and ~256-cell, but not in early or late blastula spindles. c, d Quantification of spindle length (c) and width (d) in indicated stages. n = 18, 31, 50, 54, 50, 87, 64, and 51 for (c) and n = 18, 29, 51, 58, 58, 50, 50, and 54 for (d) from 1-cell to late blastula stages, respectively, from 18 different embryos. e Cell diameter and spindle length are plotted as colored circles for individual embryos at different stages, showing spindle length scales with cell diameters after 16-cell stages. f Quantification of the max value of EGFP-α-tubulin intensity on spindle MTs relative to that on astral MTs from 2 or 4 cell spindles. g Left: live-cell images of control (top) and nocodazole-treated (bottom) spindles in metaphase. Right: an enlarged image showing k-fiber- and bridging-fiber-like bundled MTs at the spindle center. h Live-cell images of a metaphase spindle after cold treatment. i An image of a metaphase spindle after fixation showing k-fiber- and bridging-fiber-like bundled MTs at the spindle center. Error bars indicate mean ± SD. Scale bars = 100 μm (a, h) and 10 μm (g, i). Source data for (b–f) are provided as a Source Data file. One-way ANOVA with Dunnett’s multiple comparisons test was performed for (c, d, f). **p < 0.01, ***p < 0.001 and ****p < 0.0001.