The budding yeast protein kinase Ipl1/Aurora allows the absence of tension to activate the spindle checkpoint

Abstract

The spindle checkpoint prevents cell cycle progression in cells that have mitotic spindle defects. Although several spindle defects activate the spindle checkpoint, the exact nature of the primary signal is unknown. We have found that the budding yeast member of the Aurora protein kinase family, Ipl1p, is required to maintain a subset of spindle checkpoint arrests. Ipl1p is required to maintain the spindle checkpoint that is induced by overexpression of the protein kinase Mps1. Inactivating Ipl1p allows cells overexpressing Mps1p to escape from mitosis and segregate their chromosomes normally. Therefore, the requirement for Ipl1p in the spindle checkpoint is not a consequence of kinetochore and/or spindle defects. The requirement for Ipl1p distinguishes two different activators of the spindle checkpoint: Ipl1p function is required for the delay triggered by chromosomes whose kinetochores are not under tension, but is not required for arrest induced by spindle depolymerization. Ipl1p localizes at or near kinetochores during mitosis, and we propose that Ipl1p is required to monitor tension at the kinetochore. The accurate propagation of genetic information depends on faithful chromosome segregation. Accurate chromosome segregation depends on the precise coordination of events in the chromosome cycle. When chromosomes replicate during S phase, linkage between the sister chromatids (cohesion) is established and must be maintained while chromosomes condense and align on the mitotic spindle. Chromosomes attach to the mitotic spindle by their kinetochores, specialized protein structures that are assembled on centromeric DNA sequences. Once all the chromosomes are correctly aligned on the mitotic spindle, sister chromatid cohesion must dissolve promptly at anaphase to allow the sister chromatids to segregate rapidly to opposite poles of the mitotic spindle. Defects in any of these steps can result in aneuploidy, a hallmark of tumor cells and some birth defects (Lengauer et al. 1997.The spindle checkpoint prevents cells from separating their sister chromatids until chromosome alignment is complete. The conserved components of the checkpoint include the Mad (Mad1-Mad3) proteins, Bub1 and Bub3, Mps1 (a protein kinase), and Cdc55 (Hoyt et al. 1991;Li and Murray 1991;Minshull et al. 1996;Weiss and Winey 1996;Wang and Burke 1997). A separate control, the Bub2-dependent checkpoint, monitors a second aspect of chromosome segregation, the delivery of DNA or a spindle pole body into the daughter cell (Alexandru et al. 1999;Fesquet et al. 1999;Fraschini et al. 1999;Li 1999). Spindle checkpoint defects are associated with genetic instability, and some human cancers contain mutant spindle checkpoint genes (Cahill et al. 1998;Takahashi et al. 1999) The spindle checkpoint monitors the interaction between kinetochores and microtubules. Spindle checkpoint proteins localize to kinetochores (Chen et al. 1996;Taylor and McKeon 1997;Bernard et al. 1998), and all known kinetochore and spindle defects that activate the checkpoint affect the i...

Temporal changes in Hec1 phosphorylation control kinetochore–microtubule attachment stability during mitosis

“…Inhibition of Aurora B kinase results in an increase in syntelic and merotelic attachments in cultured cells (Ditchfield et al, 2003;Hauf et al, 2003;Lampson and Kapoor, 2005;Cimini et al, 2006;Knowleton et al, 2006), and decreased Aurora B kinase activity leads to hyper-stable kinetochore-MTs . Furthermore, the budding yeast Aurora kinase homolog Ipl1 has been shown to induce kinetochore-MT detachment in response to decreased tension (Pinsky et al, 2006;Biggins and Murray, 2001;Tanaka et al, 2002). Together, these results suggest that Aurora B kinase promotes detachment of incorrectly attached MTs by reducing the stability of kinetochore-MTs.…”

SAC‐ing mitotic errors: How the spindle assembly checkpoint (SAC) plays defense against chromosome mis‐segregation

“…Ipl1p/Aurora is a kinetochore-associated protein kinase required for the biorientation of sister chromatids [Pinsky et al, 2003] and for the SAC response to a lack of tension across sister kinetochores [Biggins and Murray, 2001]. The Ndc10 kinetochore protein and the Ndc80p kinetochore complex are also required for SAC function in budding yeast [Janke et al, 2001;McCleland et al, 2003;Poddar et al, 2004;Tavormina and Burke 1998].…”

“…Although stabilization of microtubules in mammalian cells with drugs such as taxol decreases tension across sister kinetochores and activates the SAC, these treatments do not visibly alter microtubule attachment to kinetochores [Skoufias et al, 2001;Waters et al, 1998]. The SAC also appears to monitor tension across sister chromatids in budding yeast, and Ipl1p is required for this response but not for SAC activation in response to a loss of kinetochoremicrotubule attachment [Biggins and Murray, 2001]. Although it is possible that Ipl1p destabilizes microtubule attachments to kinetochores that lack tension, thereby producing unattached kinetochores that activate the SAC [Tanaka et al, 2002], additional evidence that a lack of tension can signal spindle checkpoint activation in S. cerevisiae is provided by an experiment in which inhibition of DNA replication ensures that cells have only unpaired chromatids [Stern and Murray, 2001].…”

La mitose sous surveillance

“…Dans ces mutants, le point de contrôle est donc en activité et sensible à l'absence de tension. Cet arrêt dépend bien de Mad2 et -contrairement à l'arrêt produit par le nocodazole -de la protéine kinase Ipl1 (appartenant à la famille des protéine kinases Aurora) [32,33] tinguer les mutants Bub1, dont les cellules entrent en anaphase avant que tous les kinétochores ne soient correctement attachés [34], et les mutants Rod et Zw10, où l'anaphase commence après l'attachement de tous les kinétochores, mais avant l'alignement de tous les chromosomes [18]. Chez les vertébrés, un blocage en méta-phase peut également être obtenu par des agents qui altèrent la dynamique du fuseau, sans le détruire.…”