Loss of Cen-RNA activates SAC by breaking centromeric DNA. Normally, bivalents are stretched by microtubules at late metaphase and aligned properly at the metaphase plate. The SAC signal is turned off, and the APC is activated for the completion of meiosis I (left). However, Cen-RNAs reduction leads to damaged centromeres and unattached kinetochores (dashed square), which activates the SAC and restrains APC to arrest oocyte at meiosis I (right).