Cellular response upon proliferation in the presence of an active mitotic checkpoint

Abstract

Eukaryotic cells treated with microtubule-targeting agents activate the spindle assembly checkpoint to arrest in mitosis and prevent chromosome mis-segregation. A fraction of mitotically arrested cells overcomes the block and proliferates even under persistent checkpoint-activating conditions. Here, we asked what allows proliferation in such unfavourable conditions. We report that yeast cells are delayed in mitosis at each division, implying that their spindle assembly checkpoint remains responsive. The arrest causes their cell cycle to be elongated and results in a size increase. Growth saturates at mitosis and correlates with the repression of various factors involved in translation. Contrary to unperturbed cells, growth of cells with an active checkpoint requires Cdh1. This peculiar cell cycle correlates with global changes in protein expression whose signatures partly overlap with the environmental stress response. Hence, cells dividing with an active checkpoint develop recognisable specific traits that allow them to successfully complete cell division notwithstanding a constant mitotic checkpoint arrest. These properties distinguish them from unperturbed cells. Our observation may have implications for the identification of new therapeutic windows and targets in tumors.

Epistasis, aneuploidy, and gain-of-function mutations underlie the evolution of resistance to induced microtubule depolymerization

“…Regardless of the prolonged mitotic arrest, many cells slip through and continue proliferating. Cell division, however, takes place when microtubules are not properly polymerized and thus chromosomes tend to missegregate [32], which we confirmed by following the inheritance of GFP-tagged chromosome V by live cell imaging during the first cycle after decreasing temperature ( Figure S1B). Hence, we interpreted the initial slow growth rate as a consequence of prolonged activation of the mitotic checkpoint.…”

“…Thus, average size can be used as a proxy for checkpoint activation. [32]. Accordingly, we observed that ancestors tub2-401 were larger than controls expressing TUB2.…”

“…We evolved haploid yeasts carrying the tub2-401 allele ( Figure S1A). At low temperature, these cells are unable to properly polymerize microtubules [29,30] and activate the mitotic checkpoint [32]. We grew them at an intermediate temperature (18 °C), where cells can still proliferate, albeit less efficiently than wild types.…”

“…At low temperature, cell cycle progression of tub2-401 is delayed in mitosis [32]. Regardless of the prolonged mitotic arrest, many cells slip through and continue proliferating.…”

Epistasis, aneuploidy, and functional mutations underlie evolution of resistance to induced microtubule depolymerization

“…At low temperature, it is non‐functional and results in improper microtubule polymerization (Huffaker et al , 1988; Sullivan & Huffaker, 1992). This leads to the activation of both the mitotic checkpoint (Corno et al , 2019) and the spindle position checkpoint, since deletion of two of their essential genes ( MAD2 and BUB2 , respectively) impairs growth even at the semi‐permissive temperature of 23°C (Fig EV1B). By using live‐cell imaging at the restrictive temperature (18°C), we confirmed that cells were large and budded, a phenotype typical of mitotic arrest (Movie EV1).…”