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Heldt2018 - Budding yeast size control by titration of nuclear sites

ABSTRACT: This model is decribed in the article: Dilution and titration of cell-cycle regulators may control cell size in budding yeast Frank S. Heldt, Reece Lunstone, John J. Tyson, Bela Novak PLoS Comput Biol, October 2018, 14(10), e1006548, doi: 10.1371/journal.pcbi.1006548 Abstract: The size of a cell sets the scale for all biochemical processes within it, thereby affecting cellular fitness and survival. Hence, cell size needs to be kept within certain limits and relatively constant over multiple generations. However, how cells measure their size and use this information to regulate growth and division remains controversial. Here, we present two mechanistic mathematical models of the budding yeast (S. cerevisiae) cell cycle to investigate competing hypotheses on size control: inhibitor dilution and titration of nuclear sites. Our results suggest that an inhibitor-dilution mechanism, in which cell growth dilutes the transcriptional inhibitor Whi5 against the constant activator Cln3, can facilitate size homeostasis. This is achieved by utilising a positive feedback loop to establish a fixed size threshold for the START transition, which efficiently couples cell growth to cell cycle progression. Yet, we show that inhibitor dilution cannot reproduce the size of mutants that alter the cell’s overall ploidy and WHI5 gene copy number. By contrast, size control through titration of Cln3 against a constant number of genomic binding sites for the transcription factor SBF recapitulates both size homeostasis and the size of these mutant strains. Moreover, this model produces an imperfect ‘sizer’ behaviour in G1 and a ‘timer’ in S/G2/M, which combine to yield an ‘adder’ over the whole cell cycle; an observation recently made in experiments. Hence, our model connects these phenomenological data with the molecular details of the cell cycle, providing a systems-level perspective of budding yeast size control.

SUBMITTER: Frank Stefan Heldt

PROVIDER: MODEL1803220002 | BioModels | 2019-01-09

REPOSITORIES: BioModels

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			Action	DRS
	MODEL1803220002?filename=Heldt2018_YeastSizeControl_TitrationOfNuclearSites.cps	Other
	MODEL1803220002?filename=Heldt2018_YeastSizeControl_TitrationOfNuclearSites.xml	Xml

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Project description:This a model from the article: Mathematical model of the morphogenesis checkpoint in budding yeast. Ciliberto A, Novak B, Tyson JJ J. Cell Biol. [2003 Dec; Volume: 163 (Issue: 6 )] Page info: 1243-54 14691135 , Abstract: The morphogenesis checkpoint in budding yeast delays progression through the cell cycle in response to stimuli that prevent bud formation. Central to the checkpoint mechanism is Swe1 kinase: normally inactive, its activation halts cell cycle progression in G2. We propose a molecular network for Swe1 control, based on published observations of budding yeast and analogous control signals in fission yeast. The proposed Swe1 network is merged with a model of cyclin-dependent kinase regulation, converted into a set of differential equations and studied by numerical simulation. The simulations accurately reproduce the phenotypes of a dozen checkpoint mutants. Among other predictions, the model attributes a new role to Hsl1, a kinase known to play a role in Swe1 degradation: Hsl1 must also be indirectly responsible for potent inhibition of Swe1 activity. The model supports the idea that the morphogenesis checkpoint, like other checkpoints, raises the cell size threshold for progression from one phase of the cell cycle to the next. The model reproduces Fig 3 of the paper. This model originates from BioModels Database: A Database of Annotated Published Models (http://www.ebi.ac.uk/biomodels/). It is copyright (c) 2005-2011 The BioModels.net Team. For more information see the terms of use . To cite BioModels Database, please use: Li C, Donizelli M, Rodriguez N, Dharuri H, Endler L, Chelliah V, Li L, He E, Henry A, Stefan MI, Snoep JL, Hucka M, Le Novère N, Laibe C (2010) BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. BMC Syst Biol., 4:92.

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Heldt2018 - Budding yeast size control by titration of nuclear sites

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