Figure 6. Resolution of the X chromosome to one side correlates with an asymmetry of microtubules.

(A) Left: three-dimensional model of an anaphase I spindle and definition of two equal volumes on opposite sides of the X chromosome. Right: Measurement of total polymer length within selected volumes of 1 µm³. (B) Graph showing the ratio of both volumetric measurements plotted against the autosome-to-autosome distance for the meiotic stages as shown in Figures 3 and 4 and Appendix 1—figure 4. A trend line was fitted to illustrate the increase in the asymmetry. (C) Deconstructed 3D model (data set anaphase no. 3) illustrating the microtubules associated with each side of the X chromosome (red), named pos. 1 (green) and pos. 2 (blue). Centrioles are shown in purple, microtubules not connected to the spindle poles in yellow. Scale bar, 500 nm. (D) Table showing the autosome 1-to-autosome 2 distance (A1, A2), the total number of microtubules for both positions and the calculated ratio for each data set (see Figures 3 and 4 and Appendix 1—figure 4 (data sets shown in parentheses)). (E) Upper panel: Maximum intensity projection images from live imaging showing microtubules labeled with β-tubulin::GFP (white) and chromosomes with histone H2B::mCherry (red). Time is given relative to the onset of X chromosome segregation (t = 0). Scale bar, 2 µm. Lower panel: Illustration of the measurement of fluorescence intensity in two volumes (V1, V2) of 1 µm³ at opposite sides of the X chromosome (red). Autosomes are in blue, microtubules in green. (F) Ratio of fluorescence intensities as measured in (E). Upper panel: autosomes 1-to-autosomes two distance (A1-A2, red) and autosomes 1-to-X chromosome distance (A1-X, blue) over time. Solid lines show the mean, shaded areas indicate the standard deviation. The onset of X chromosome movement is given as time point zero (t = 0). Lower panel: ratio of fluorescence intensities (V1/V2) for corresponding time points (black, time is relative to the onset of segregation of the X chromosome, t = 0; n = 5).