A Gradient in Metaphase Tension Leads to a Scaled Cellular Response in Mitosis

Abstract

Graphical AbstractHighlights d The magnitude of centromere tension is sensed by the cell during mitosis d The cellular response to low metaphase tension is dose dependent in nature d The primary cellular response to low metaphase tension is detachment of kinetochores d Tension-dependent phosphorylation of the kinetochore underlies the tension response SUMMARY During mitosis, motor proteins associate with microtubules to exert pushing forces that establish a mitotic spindle. These pushing forces generate opposing tension in the chromatin that connects oppositely attached sister chromatids, which may then act as a mechanical signal to ensure the fidelity of chromosome segregation during mitosis. However, the role of tension in mitotic cellular signaling remains controversial. In this study, we generated a gradient in tension over multiple isogenic budding yeast cell lines by genetically altering the magnitude of motor-based spindle forces. We found that a decreasing gradient in tension led to an increasing gradient in the rates of kinetochore detachment and anaphase chromosome mis-segregration, and in metaphase time. Simulations and experiments indicated that these tension responses originate from a tension-dependent kinetochore phosphorylation gradient. We conclude that the cell is exquisitely tuned to the magnitude of tension as a signal to detect potential chromosome segregation errors during mitosis.

Relax, Kinetochores Are Exquisitely Sensitive to Tension

“…By estimating the absolute levels of tension at kinetochores in dividing yeast cells and relating these measurements to kinetochore detachment probability, Mukherjee et al (2019) quantify in this issue of Developmental Cell the force sensitivity of the mitotic error correction system.…”

“…Building on previous work from the same lab (Chacó n et al, 2014), Mukherjee et al (2019) use a combination of genetic approaches and live-cell imaging to manipulate and quantify kinetochore tension in budding yeast. The authors find that kinetochores are highly responsive to tension.…”

“…A key assumption is that the fluctuations are driven solely by thermal energy and not by active (energy-transducing) external processes, such as microtubule or molecular motor dynamics. To avoid the latter possibilities, Mukherjee et al (2019) measured fluctuations over very short (1 s) time intervals during which active motility made an apparently negligible contribution (Chacó n et al, 2014;Mukherjee et al, 2019). With the stiffness k in hand, the authors then measured the distance between sister lacO spots, Dx, and computed inter-kinetochore force using Hooke's law, F = k$Dx.…”

“…In wild-type budding yeast, the estimated pericentromere tension was 5 pN, enough to provide a useful mechanical signal (Chacó n et al, 2014). Mukherjee et al (2019) also use kinesin-5 deficient yeast strains to perturb tension across the pericentromere. Kinesin-5 motors normally help establish and maintain spindle bipolarity by crosslinking and sliding interpolar microtubules, thereby generating outward forces that are transmitted to chromosomes via kinetochoreattached microtubules (Lampson et al, 2004).…”

“…This fail-safe system delays mitotic progression by inhibiting the metaphase-to-anaphase transition (Biggins and Murray, 2001). As further validation, Mukherjee et al (2019) examined whether or not the mutant cells with reduced tension tended to mis-segregate their chromosomes when permitted to enter anaphase. Cells from which both Mad2 and Cin8 were deleted (thereby disabling the spindle checkpoint response) displayed high levels of anaphase chromosome mis-segregation, consistent with the low-tension mutants having high kinetochore-microtubule detachment rates.…”