Stochastic Modeling Yields a Mechanistic Framework for Spindle Attachment Error Correction in Budding Yeast Mitosis

AbstractTo divide replicated chromosomes equally between daughter cells kinetochores must attach to microtubules emanating from opposite poles of the mitotic spindle. Two mechanisms, namely, error correction and ‘spindle assembly checkpoint’ work together to facilitate this process. The error correction mechanism recognizes and detaches erroneous kinetochore-microtubule attachments, and the spindle assembly checkpoint delays the onset of anaphase until all the kinetochores are properly attached. Kinases and phosphatases at the kinetochore play a key role in proper functioning of these two mechanisms. Here we present a stochastic model to study how the opposing activities of kinases and phosphatases at the kinetochore affect error correction of kinetochore-microtubule attachments and checkpoint signaling in budding yeast, Saccharomyces cerevisiae. We show that error correction and biorientation of chromosomes occurs efficiently when the ratio between kinase activity of Ipl1 and the activity of an opposing phosphatase is a constant (balance point), and derive an approximate analytical formula that defines the balance point. Analysis of the coupling of the spindle assembly checkpoint signal to error correction shows that its strength remains high when the Ipl1 activity is equal to (or larger than) the value specified by the balance point, and the activity of another kinase, Mps1, is much larger (approximately 30 times larger) than its opposing phosphatase (PP1). We also find that the geometrical orientation of sister chromatids does not significantly improve the probability of their reaching biorientation, which depends entirely on Ipl1-dependent microtubule detachment.Author summaryThe kinetochore, the master regulator of chromosome segregation, integrates signals from different chromosome attachment states to generate an appropriate response, like the destabilization of erroneous kinetochore-microtubule attachments, stabilization of correct attachments, maintenance of the spindle assembly checkpoint signal until all kinetochores are properly attached, and finally silencing of checkpoint when biorientation is achieved. At a molecular level the job is carried out by kinases and phosphatases. The complexity of the interactions between these kinases and phosphatases makes intuitive analysis of the control network impossible, and a systems-level model is needed to put experimental information together and to generate testable hypotheses. Here we present such a model for the process of error correction and its coupling to the spindle assembly checkpoint in budding yeast. Using the model, we characterize the balance between kinase and phosphatase activities required for removing erroneous attachments and then establishing correct stable attachments between kinetochore and microtubule. We also analyze how the balance affects the strength of the spindle assembly checkpoint signal.

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chTOG is a conserved mitotic error correction factor

10.1101/2020.08.03.235325 ◽

2020 ◽

Author(s):

Jacob A. Herman ◽

Matthew P. Miller ◽

Sue Biggins

Keyword(s):

Protein Kinase ◽

Error Correction ◽

Chromosome Segregation ◽

Correction Factor ◽

Budding Yeast ◽

Aurora B ◽

Spindle Poles ◽

Low Tension ◽

Intrinsic Error

AbstractAccurate chromosome segregation requires kinetochores on duplicated chromatids to biorient by attaching to dynamic microtubules from opposite spindle poles, which exerts forces to bring kinetochores under tension. However, kinetochores initially bind to MTs indiscriminately, resulting in errors that must be corrected. While the Aurora B protein kinase destabilizes low-tension attachments by phosphorylating kinetochores, low-tension attachments are intrinsically less stable than those under higher tension in vitro independent of Aurora activity. Intrinsic tensionsensitive behavior requires the microtubule regulator Stu2 (budding yeast Dis1/XMAP215 ortholog), which we demonstrate here is likely a conserved function for the TOG protein family. The human TOG protein, chTOG, localizes to kinetochores independent of microtubules by interacting with Hec1. We identify a chTOG mutant that regulates microtubule dynamics but accumulates erroneous kinetochore-microtubule attachments that Aurora B fails to destabilize. Thus, TOG proteins confer a unique, intrinsic error correction activity to kinetochores that ensures accurate chromosome segregation.

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Shugoshin biases chromosomes for biorientation through condensin recruitment to the pericentromere

eLife ◽

10.7554/elife.01374 ◽

2014 ◽

Vol 3 ◽

Cited By ~ 44

Author(s):

Kitty F Verzijlbergen ◽

Olga O Nerusheva ◽

David Kelly ◽

Alastair Kerr ◽

Dean Clift ◽

...

Keyword(s):

Error Correction ◽

Molecular Basis ◽

Budding Yeast ◽

Aurora B ◽

Aurora B Kinase ◽

Dual Roles ◽

Sister Kinetochore

To protect against aneuploidy, chromosomes must attach to microtubules from opposite poles (‘biorientation’) prior to their segregation during mitosis. Biorientation relies on the correction of erroneous attachments by the aurora B kinase, which destabilizes kinetochore-microtubule attachments that lack tension. Incorrect attachments are also avoided because sister kinetochores are intrinsically biased towards capture by microtubules from opposite poles. Here, we show that shugoshin acts as a pericentromeric adaptor that plays dual roles in biorientation in budding yeast. Shugoshin maintains the aurora B kinase at kinetochores that lack tension, thereby engaging the error correction machinery. Shugoshin also recruits the chromosome-organizing complex, condensin, to the pericentromere. Pericentromeric condensin biases sister kinetochores towards capture by microtubules from opposite poles. Our findings uncover the molecular basis of the bias to sister kinetochore capture and expose shugoshin as a pericentromeric hub controlling chromosome biorientation.

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