Homologue disjunction in mouse oocytes requires proteolysis of securin and cyclin B1

Disjunction of pairs of homologous chromosomes during the first meiotic division (MI) requires anaphase-promoting complex (APC)-mediated activation of separase in budding yeast(1,2) and Caenorhabditis elegans(3,4,5), but not Xenopus laevis(6,7). It is not clear which model best fits the mammalian system. Here we show that homologue disjunction in mouse oocytes is dependent on proteolysis of the separase inhibitor securin and the Cdk1 regulatory sub-unit cyclin B1. Proteolysis of both proteins was entirely dependent on their conserved destruction box (D-box) motifs, through which they are targeted to the APC(8). These data indicate that the mechanisms regulating homologue disjunction in mammalian oocytes are similar to those of budding yeast and C. elegans.