Plk4 OE oocytes have impaired progression into meiosis I owing to SAC activation. (A) Kinetics of PBE extrusion in controls (black curves) and Plk4 OE (blue curves) oocytes from line A upon treatment (dotted curves) or not (plain curves) with 100 nM Reversine at NEBD; n is the number of oocytes; PBE mean times are 9h05 for controls, 10h50 for Plk4 OE, 6h43 for controls treated by Reversine, and 6h41 for Plk4 OE treated by Reversine. Tukey’s multiple comparison test: **, P < 0.01 for controls vs. Plk4 OE; ****, P < 0.0001 for controls vs. controls + Reversine, controls vs. Plk4 OE + Reversine, Plk4 OE vs. controls + Reversine, and Plk4 OE vs. Plk4 OE + Reversine. Controls + Reversine and Plk4 OE + Reversine are not significantly different. (B) Live image of a Plk4 OE oocyte (line A) presenting a DNA fragment (chromosomes labeled with histone-GFP) which can be observed on the left picture (black arrow) and that nonetheless extrudes a first polar body at NEBD + 9h30 (PBE, white arrow and white star). Scale bar is 10 µm for the left panel and 20 µm for the other panels. Time points are in hours and minutes after NEBD. The emerging first polar body is highlighted by a white star. (C) Evidence for structural defects in chromosome segregation in Plk4 OE oocytes. Plk4 OE oocyte from line A, observed at NEBD + 8h00, undergoing anaphase I where DNA (white) and MT (green) are labeled. We can clearly observe the smallest DNA fragment lagging in between the two sets of univalents (red arrow) and the largest DNA fragment being separated into two deleted univalents, each retained in the oocyte (two red arrowheads). The stars indicate the position of the polar body starting to be emitted. Scale bar is 10 µm.