Determinants of robustness in spindle assembly checkpoint signalling

Abstract

The spindle assembly checkpoint is a conserved signalling pathway that protects genome integrity. Given its central importance, this checkpoint should withstand stochastic fluctuations and environmental perturbations, but the extent of and mechanisms underlying its robustness remain unknown. We probed spindle assembly checkpoint signalling by modulating checkpoint protein abundance and nutrient conditions in fission yeast. For core checkpoint proteins, a mere 20% reduction can suffice to impair signalling, revealing a surprising fragility. Quantification of protein abundance in single cells showed little variability (noise) of critical proteins, explaining why the checkpoint normally functions reliably. Checkpoint-mediated stoichiometric inhibition of the anaphase activator Cdc20 (Slp1 in Schizosaccharomyces pombe) can account for the tolerance towards small fluctuations in protein abundance and explains our observation that some perturbations lead to non-genetic variation in the checkpoint response. Our work highlights low gene expression noise as an important determinant of reliable checkpoint signalling.

miR-28-5p Promotes Chromosomal Instability in VHL-Associated Cancers by Inhibiting Mad2 Translation

“…Thus, miR-28-5p-mediated regulation of Mad2 may normally be dedicated to fine-tune Mad2 levels to balance against stressinduced numerical chromosomal instability. This interpretation is in line with recent findings that amounts of checkpoint proteins dictate the strength of the mitotic checkpoint (35)(36)(37). Accordingly, miR-28-5p may be part of a mechanisms that provides robustness to the process of mitosis assuring errorfree chromosome segregation.…”

The TRAF-interacting protein (TRAIP) is a regulator of the spindle assembly checkpoint

“…The expression and/or localization of SAC proteins are finely modulated to regulate APC/C activity (Musacchio and Salmon, 2007) in a dose-dependent manner (Collin et al, 2013;Heinrich et al, 2013). The robustness of the SAC is, in part, determined by the amount of MAD2 recruited to kinetochores.…”

“…4E,F). This might be physiologically relevant, because a reduction of 20% in MAD2 levels is sufficient to impair SAC activity in yeast (Heinrich et al, 2013).…”

“…APC/C activity is regulated by the spindle assembly checkpoint (SAC) proteins MAD1, MAD2 (also known as MAD1L1, MAD2L1, respectively), BUBR1 (also known as BUB1B), BUB1, BUB3 and MPS1 (also known as TTK), which sense whether or not chromosomes are connected in a bi-oriented manner to opposite spindle poles through microtubules (Foley and Kapoor, 2013;Khodjakov and Pines, 2010;Santaguida and Musacchio, 2009). The strength of the SAC crucially depends on the MAD2 abundance at kinetochores (Collin et al, 2013;Heinrich et al, 2013). Defects in chromosome segregation control cause chromosomal instability and aneuploidy, common characteristics of human solid tumors (Holland and Cleveland, 2012).…”

The Cdc20-binding Phe Box of the Spindle Checkpoint Protein BubR1 Maintains the Mitotic Checkpoint Complex During Mitosis

“…Recent studies have shown that the length of mitotic arrest and presumably the strength of the spindle checkpoint can be tuned by the number of unattached kinetochores or the severity of spindle damage (41)(42)(43). We wondered whether the Phe and D boxes of BubR1 were required for the less robust mitotic arrest triggered by low concentrations of taxol (Fig.…”