Fig. 4: A Mathematical model of MI spindle migration.

a Illustration of the coordinate system of the spindle, actin filaments, and mitochondria. The ER, which carries FMN2, is assumed to attach to the spindle at all time. More details of the model can be found in the section “Methods”. b Force balance on each actin filament. c Top: illustration of the repulsion and attraction force among mitochondria and between the spindle and mitochondria. Bottom: Diagram of the repulsion and attraction force as a function of distance d. d Trajectory of the center of the spindle in the control case. e–g Simulations showing the relative position of the spindle and the mitochondria distribution at three different time points as marked in the trajectory in d. e Initial state, f starting migration, g mid-way of migration. Note that due to their very short length, actin filaments are not visible in these representations. h Model for myosin Vb tail expression. i Model for Drp1 knockdown. j Representative time-lapse images of mitochondria distribution during spindle migration in control siRNA-injected (n = 29), Drp1 siNRA-injected (n = 23), myosin Vb tail-expressing (n = 22), MFN1 over-expressing (OE) (n = 27), or Myosin Vb tail-Acta-expressing oocytes (n = 37). Green, mitochondria. Magenta, chromosomes. Scale bar, 20 µm. k, l Centroids of chromosomes were tracked in oocytes and the movement of chromosomes position were plotted in Drp1 siRNA-injected, myosin Vb tail-expressing (k), MFN1 OE, or myosin Vb tail-Acta-expressing (l) oocytes. Data are represented as mean ± SD, from three independent experiments. Oocyte numbers are indicated in brackets. m Quantification of the percentage of oocytes that underwent spindle migration for WT oocyte, Drp1 siRNA-injected, MFN1OE, myosin Vb tail-expressing, and myosin Vb tail-ActA-expressing oocytes. See Supplementary Fig. 6a, b for the efficiency of Drp1 knockdown. Data are represented as mean ± SD. Data are from three independent experiments. One side ANOVA, Tukey’s multiple comparisons test. Data are represented as mean ± SD. Oocyte numbers are indicated in brackets. Source data are provided as a Source Data file.