Figure 8.

Cooperation among Ran, Aurora A, and Plk4 in regulating bivalent movement and congression toward the metaphase I plate. (A) Time-lapse imaging of oocytes expressing histone H2B-mRFP (inverted, black). Shown are the first 4 h of meiosis I after NEBD for controls; oocytes treated with 2 µM centrinone, 1 µM Aurora A inhibitor 1 (AurA Inh 1), or 1 µM VX-680; and oocytes expressing dominant-negative RanT24N. Three phases of chromosome movement (collapse, outward expansion, and bivalent congression) are indicated. (B) Representative chromosome tracks of the outward expansion for each indicated condition. Directionality and distance of movement is represented by the angle and length of the arrows, respectively; arrow thicknesses illustrate speeds. (C) Schematic representation of chromosome distributions at their maximum expansion, as quantified in E. Mean values for major and minor axes for each condition are shown (±SEM). (D) Violin plots depicting the frequency distribution of mean velocity of chromosome movements, which is significantly reduced as a result of Plk4 and Aurora A inhibition. (E) Fitting of the chromosome end coordinates at their maximal expansion to an ellipse. Control, RanT24N-expressing, and centrinone-treated samples display an isotropic distribution of chromosomes that tends to a 2D circle (ratio between major and minor axis approximates 1). In oocytes treated with Aurora A inhibitor 1 or VX-680, chromosomes show a preferential expansion direction along the axis of spindle, indicated by a ratio between major and minor axis of the fitted ellipse that is higher than 1 and significantly differs from the control (see Materials and methods; ***, P < 0.001).