Translation is required for MII transition, but it does not affect spindle morphology. (A) Selected frames from a time-lapse recording of an oocyte injected with H1-Alexa647 (red) and HiLyte488-tubulin (cyan) to label chromosomes and microtubules, respectively. The oocyte was imaged through meiosis on a spinning disk confocal microscope. Before inducing maturation, the oocyte was treated with 10 µM emetine to block translation. Maximum intensity projections are shown, the scale bar is 20 µm, and time is given in minutes. PB I denotes the first polar body, and PN is the pronucleus. (B) Oocytes fixed at metaphase I and stained for microtubules (anti-tubulin, cyan), chromatin (Hoechst 33342, red). Oocytes were treated with emetine and DMSO or 20 µM U0126. 3D stacks were acquired on a spinning disk microscope. Maximum intensity projections are shown; scale bars are 20 µm. (C and D) Boxplots showing a comparison of the pole-to-pole distance and maximal length of microtubules at metaphase I between emetine and emetine+U0126-treated oocytes as shown on (B). Statistical comparison was done using a two-tailed t test. (E) Mos–MAPK specifically downregulates PCM proteins, reduces the growth and number of astral and interpolar microtubules, and prevents anaphase B, thereby minimizing the size of the polar body. Bottom: schematic illustration of correlated changes in aster size and pole distance. Mean values shown on Fig. 4, B and C are plotted on a schematic of the spindle.