Fragmented aMTOCs have increased MT-nucleating activity at NEBD. (A) EB3-GFP expression in control (left) and Plk4 OE (right) oocytes observed at NEBD. The black dotted square shows the mCherry-Plk4 labeling (pink) that surrounds early spindle MT, visible only in Plk4 OE oocytes. EB3-GFP appears in gray levels. Scale bar is 10 µm. (B) Normalized signal intensity of EB3-GFP around chromosomes in control (black dots) and Plk4 OE (blue squares) oocytes observed at NEBD. The signal was measured in a Ø20-µm region around the chromosomes; total signal intensity was measured in a Ø70-µm region covering the whole oocyte. Normalized signal intensity is the ratio of local/total intensity measured for individual oocytes; ****, P < 0.0001. (C) Correlation between the number of aMTOCs in prophase I and normalized fluorescence intensity of EB3-GFP at NEBD (n = 37). Normalized EB3-GFP fluorescence intensity measured at NEBD is plotted against the number of aMTOCs per oocyte in prophase I. (D) Early steps of spindle formation in control versus Plk4 OE oocytes expressing EB3-GFP. Oocytes were followed from prophase I exit until spindle bipolarization. EB3-GFP appears white and mCherry-Plk4 pink. Scale bar is 15 µm. Timing (expressed in hours and minutes) is relative to NEBD. (E) Timing of spindle bipolarization observed in living oocytes expressing EB3-GFP as presented in D; **, P = 0.0076. For B and E, the statistical tests used are two-tailed t test with Welch correction, and n corresponds to the number of oocytes. Error bars correspond to SD.