Overexpression of Mad2 leads to chromosome missegregations in meiosis I.

<p>(A) Schematic outline of the experimental procedure. Oocytes arrested in GV stage are injected with mRNA encoding GFP-tagged Mad2, and released to undergo meiotic maturation. Oocytes that extrude a PB are examined for GFP-Mad2 expression by fluorecence microscopy, and those expressing detectable levels of Mad2 are used for chromosome spreads. The experiment was repeated 4 times. (B) Percentage of oocytes bypassing the metaphase I arrest with moderate GFP-Mad2 expression. (C) Percentage of aneuploidies in metaphase II (gain or loss of one or more univalent chromosomes) of oocytes injected with injection buffer (control), or GFP-Mad2 mRNA (same as in (B)). (D) Model to explain the observed phenotypes after changing Mad2 levels. See text for details.