Preventing cyclin B synthesis blocks MII transition, but it does not affect MI spindle morphology. (A) Selected frames from a time-lapse recording of oocytes injected with H1-Alexa647 (red) and HiLyte488-tubulin (cyan) to label chromosomes and microtubules, respectively. Oocytes were imaged through meiosis on a spinning disk confocal microscope. Before inducing maturation, oocytes were injected with either a morpholino targeting cyclin B or water as control. Maximum intensity projections are shown, scale bars are 20 µm, and time is given in minutes. PB I and II denote the first and second polar bodies, respectively; PN is the pronucleus. (B) Individual data points and boxplots showing a comparison of the maximal length of microtubules at metaphase I between control and cyclin B morpholino-injected oocytes. Statistical comparison was done using a two-tailed t test; n is the number of oocytes analyzed.