Cell Architecture Laboratory • Kimura Group

The mitotic spindle is a diamond-shaped molecular apparatus crucial for chromosomal segregation. Previous studies suggested that the spindle can self-organize to maintain a constant aspect ratio between its length and width against physical perturbations. Here we determine the widths of metaphase spindles of various sizes observed during embryogenesis in Caenorhabditis elegans. The spindle width correlates well with the spindle length, but the aspect ratio between the spindle length and spindle width is not constant, indicating an allometric relationship between these parameters. We characterize how DNA quantity (ploidy) affects spindle shape by using haploid and polyploid embryos. On the basis of the quantitative data, we deduce an allometric equation that describes the spindle width as a function of the length of the hypotenuse and ploidy. On the basis of this equation, we propose a force-balance model to determine the spindle width.

(A) Metaphase spindles at 4 representative cell stages (Bar = 5 μm). (B) The spindle width (pink), half-spindle length (light blue), and hypotenuse length (orange) were shown. (C) The spindle width from diploid (blue diamond), haploid (yellow circle), and polyploid (green triangles) is plotted against the product of 0.36th-power of ploidy and 0.58th-power of hypotenuse length. (Figures were modified from the paper.)