Separase is an evolutionarily conserved
protease that is essential for chromosome segregation and cleaves
cohesin Scc1/Rad21, which joins the sister chromatids together. Although mammalian
separase also functions in chromosome segregation, our understanding of this process in mammals is still incomplete. We generated
separase knockout mice, reporting an essential function for mammalian
separase.
Separase-deficient mouse embryonic fibroblasts exhibited severely restrained increases in cell number,
polyploid chromosomes, and amplified centrosomes. Chromosome spreads demonstrated that multiple chromosomes connected to a centromeric region. Live observation demonstrated that the chromosomes of
separase-deficient cells condensed, but failed to segregate, although subsequent cytokinesis and chromosome decondensation proceeded normally. These results establish that mammalian
separase is essential for the separation of centromeres, but not of the arm regions of chromosomes. Other cell cycle events, such as mitotic exit, DNA replication, and centrosome duplication appear to occur normally. We also demonstrated that heterozygous
separase-deficient cells exhibited severely restrained increases in cell number with apparently normal mitosis in the absence of
securin, which is an inhibitory partner of
separase.