Prolonged mitosis causes separase deregulation and chromosome nondisjunction.

During mitotic chromosome segregation, the protease separase severs cohesin between sister chromatids. A probe for separase activity has shown that separase undergoes abrupt activation shortly before anaphase onset, after being suppressed throughout metaphase; however, the relevance of this control remains unclear. Here, we report that separase activates precociously, with respect to anaphase onset, during prolonged metaphase in multiple types of cancer cell lines. The artificial extension of metaphase in chromosomally stable diploid cells leads to precocious activation and, subsequently, to chromosomal bridges in anaphase, which seems to be attributable to incomplete cohesin removal. Conversely, shortening back of a prolonged metaphase restores the activation of separase and ameliorates anaphase bridge formation. These observations suggest that retarded metaphase progression affects the separase activation profile and its enzymatic proficiency. Our findings provide an unanticipated etiology for chromosomal instability in cancers and underscore the relevance of swift mitotic transitions for fail-safe chromosome segregation. • Prolonged metaphase and separase deregulation are widespread among cancer cells • Delaying anaphase onset impairs activation profile and proficiency of separase • Shortening back of prolonged metaphase restores robust separase activation kinetics • Separase deregulation results in incomplete cohesin removal and anaphase bridges Using a separase sensor, Shindo et al. show that separase is widely deregulated in cancer cells and that this deregulation is attributable to prolonged metaphase. A swift progression through metaphase to anaphase ensures characteristic sharp activation and proficiency of separase and therefore underlies faithful chromosome segregation. [ABSTRACT FROM AUTHOR]