The selective continued linkage of centromeres from mitosis to interphase in the absence of mammalian separase

Abstract

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.

Regulation of Centromeric Cohesion by Sororin Independently of the APC/C

“…36,37 Securin degradation frees separase which has been proposed to cleave the remaining cohesin at the centromeres, 38,39 permitting sister chromatid separation during anaphase. 40,41 However, recent reports have shown that the APC/C and its activator Cdc20 are dispensable for sister centromere separation. [42][43][44][45][46] These data indicated that although the APC/C plays an important role in the fidelity of anaphase, the regulation of sister chromatid separation is more complex in mammals than was previously thought (reviewed in ref.…”

Overexpression of Separase induces aneuploidy and mammary tumorigenesis

“…Dysregulation of the mitotic machinery that helps maintain chromosomal stability in mammary cells can result in aneuploidy and subsequently, cancer formation. We focused on Separase for the following reasons that have important implications for breast cancer: (i) Separase plays a central role in promoting faithful chromosome segregation; (ii) our previous studies strongly indicated that hormonal stimulation of p53-null mice mammary gland results in overexpression of the ESPL1 and Separase protein, which may be a direct cause of aneuploidy (5); and (iii) siRNA-mediated knockdown of Separase and Separase deficient mouse embryonic fibroblasts results in genomic instability (6)(7)(8).…”

t(8;21)(q22;q22) fusion proteins preferentially bind to duplicated AML1/RUNX1 DNA-binding sequences to differentially regulate gene expression

“…66 In addition to revealing the preference of AML1-ETO for duplicated AML1 sites, we also reported separase as a novel AML1-ETO target gene and used it as a model to demonstrate the regulation of AML1-ETO by multiple sites. Separase is essential for proper chromosome segregation, 67,68 and an inactivating mutation causes genomic instability and increased frequency of epithelial cancer in a zebrafish model. 69 Since separase expression is modulated in AML1-ETO-expressing U937T cells, t(8;21) patients might have deregulated separase expression that may contribute to the deregulation of the cell cycle and the associated gain and loss of chromosomes observed in these patients.…”