scholarly journals A size-invariant bud-duration timer enables robustness in yeast cell size control

2017 ◽  
Author(s):  
Corey A.H. Allard ◽  
Franziska Decker ◽  
Orion D. Weiner ◽  
Jared E. Toettcher ◽  
Brian R. Graziano
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Cell Cycle Progression ◽  
Growth Parameters ◽  
Size Control ◽  
Molecular Size ◽  
Small Cells ◽  
Cell Physiology ◽  
Temperature Sensitive ◽  
Level Control

SUMMARYCell size drives key aspects of cell physiology, including organelle abundance [1, 2] and DNA ploidy [3]. While cells employ diverse strategies to regulate size [4–11], it is unclear how they are integrated to provide robust, systems-level control. In budding yeast, a molecular size sensor restricts passage of small cells through G1, enabling them to gain proportionally more volume than larger cells before progressing to Start [7, 12, 13]. Size control post-Start is less clear. S/G2/M duration in wildtype cells shows only a weak dependence on cell size; and since yeast exhibit exponential growth, larger cells would be expected to add more volume than smaller ones [7, 14–17]. However, even large mother cells produce smaller daughters, suggesting that additional regulation may occur during S/G2/M [7]. To gain further insight into post-Start size control, we prepared ‘giant’ yeast (>10-fold larger than typical volume) using two approaches to reversibly block cell cycle progression but not growth: optogenetic disruption of the cell polarity factor Bem1 [18, 19] and a temperature-sensitive cdk1 allele [20]. We reasoned that giant yeast would satisfy pre-Start size control while enabling us to uncover post-Start size-limiting mechanisms though the identification of invariant growth parameters. Upon release from their block, giant mothers reenter the cell cycle and their progeny rapidly return to the original unperturbed size. This behavior is consistent with a size-invariant ‘timer’ specifying the duration of S/G2/M and indicates that yeast use at least two distinct mechanisms at different cell cycle phases to ensure size homeostasis.

scholarly journals Growth Rate and Cell Size Modulate the Synthesis of, and Requirement for, G1-Phase Cyclins at Start

2004 ◽  
Vol 24 (24) ◽  
pp. 10802-10813 ◽  
Author(s):  
Brandt L. Schneider ◽  
Jian Zhang ◽  
J. Markwardt ◽  
George Tokiwa ◽  
Tom Volpe ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Growth Rate ◽  
Cell Size ◽  
Cell Cycle Progression ◽  
Control Mechanism ◽  
Size Control ◽  
Small Cells ◽  
Critical Threshold ◽  
Cycle Progression

ABSTRACT In Saccharomyces cerevisiae, commitment to cell cycle progression occurs at Start. Progression past Start requires cell growth and protein synthesis, a minimum cell size, and G1-phase cyclins. We examined the relationships among these factors. Rapidly growing cells expressed, and required, dramatically more Cln protein than did slowly growing cells. To clarify the role of cell size, we expressed defined amounts of CLN mRNA in cells of different sizes. When Cln was expressed at nearly physiological levels, a critical threshold of Cln expression was required for cell cycle progression, and this critical threshold varied with both cell size and growth rate: as cells grew larger, they needed less CLN mRNA, but as cells grew faster, they needed more Cln protein. At least in part, large cells had a reduced requirement for CLN mRNA because large cells generated more Cln protein per unit of mRNA than did small cells. When Cln was overexpressed, it was capable of promoting Start rapidly, regardless of cell size or growth rate. In summary, the amount of Cln required for Start depends dramatically on both cell size and growth rate. Large cells generate more Cln1 or Cln2 protein for a given amount of CLN mRNA, suggesting the existence of a novel posttranscriptional size control mechanism.

scholarly journals Large cells activate global protein degradation to maintain cell size homeostasis

2021 ◽  
Author(s):  
Shixuan Liu ◽  
Ceryl Tan ◽  
Chloe Melo-Gavin ◽  
Kevin G. Mark ◽  
Miriam Bracha Ginzberg ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Cell Size ◽  
Cell Cycle Progression ◽  
Mapk Pathway ◽  
Cellular Growth ◽  
Small Cells ◽  
Animal Cells ◽  
Size Dependent

Proliferating animal cells maintain a stable size distribution over generations despite fluctuations in cell growth and division size. This tight control of cell size involves both cell size checkpoints (e.g., delaying cell cycle progression for small cells) and size-dependent compensation in rates of mass accumulation (e.g., slowdown of cellular growth in large cells). We previously identified that the mammalian cell size checkpoint is mediated by a selective activation of the p38 MAPK pathway in small cells. However, mechanisms underlying the size-dependent compensation of cellular growth remain unknown. In this study, we quantified global rates of protein synthesis and degradation in naturally large and small cells, as well as in conditions that trigger a size-dependent compensation in cellular growth. Rates of protein synthesis increase proportionally with cell size in both perturbed and unperturbed conditions, as well as across cell cycle stages. Additionally, large cells exhibit elevated rates of global protein degradation and increased levels of activated proteasomes. Conditions that trigger a large-size-induced slowdown of cellular growth also promote proteasome-mediated global protein degradation, which initiates only after growth rate compensation occurs. Interestingly, the elevated rates of global protein degradation in large cells were disproportionately higher than the increase in size, suggesting activation of protein degradation pathways. Large cells at the G1/S transition show hyperactivated levels of protein degradation, even higher than similarly sized or larger cells in S or G2, coinciding with the timing of the most stringent size control in animal cells. Together, these findings suggest that large cells maintain cell size homeostasis by activating global protein degradation to induce a compensatory slowdown of growth.

scholarly journals Size uniformity of animal cells is actively maintained by a p38 MAPK-dependent regulation of G1-length

2017 ◽  
Author(s):  
Shixuan Liu ◽  
Miriam B. Ginzberg ◽  
Nish Patel ◽  
Marc Hild ◽  
Bosco Leung ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
P38 Mapk ◽  
Cell Cycle Progression ◽  
Molecular Mechanisms ◽  
Mapk Pathway ◽  
Small Cells ◽  
Animal Cells ◽  
Cycle Progression ◽  
Size Uniformity

AbstractAnimal cells within a tissue typically display a striking regularity in their size. To date, the molecular mechanisms that control this uniformity are still unknown. We have previously shown that size uniformity in animal cells is promoted, in part, by size-dependent regulation of G1 length. To identify the molecular mechanisms underlying this process, we performed a large-scale small molecule screen and found that the p38 MAPK pathway is involved in coordinating cell size and cell cycle progression. Small cells display higher p38 activity and spend more time in G1 than larger cells. Inhibition of p38 MAPK leads to loss of the compensatory G1 length extension in small cells, resulting in faster proliferation, smaller cell size and increased size heterogeneity. We propose a model wherein the p38 pathway responds to changes in cell size and regulates G1 exit accordingly, to increase cell size uniformity.One-sentence summaryThe p38 MAP kinase pathway coordinates cell growth and cell cycle progression by lengthening G1 in small cells, allowing them more time to grow before their next division.

scholarly journals Cell size sensing in animal cells coordinates anabolic growth rates and cell cycle progression to maintain cell size uniformity

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Miriam Bracha Ginzberg ◽  
Nancy Chang ◽  
Heather D'Souza ◽  
Nish Patel ◽  
Ran Kafri ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Growth Rates ◽  
Cell Cycle Progression ◽  
Cellular Growth ◽  
Small Cells ◽  
Live Cells ◽  
Control Mechanisms ◽  
Animal Cells ◽  
Size Uniformity

Cell size uniformity in healthy tissues suggests that control mechanisms might coordinate cell growth and division. We derived a method to assay whether cellular growth rates depend on cell size, by monitoring how variance in size changes as cells grow. Our data revealed that, twice during the cell cycle, growth rates are selectively increased in small cells and reduced in large cells, ensuring cell size uniformity. This regulation was also observed directly by monitoring nuclear growth in live cells. We also detected cell-size-dependent adjustments of G1 length, which further reduce variability. Combining our assays with chemical/genetic perturbations confirmed that cells employ two strategies, adjusting both cell cycle length and growth rate, to maintain the appropriate size. Additionally, although Rb signaling is not required for these regulatory behaviors, perturbing Cdk4 activity still influences cell size, suggesting that the Cdk4 pathway may play a role in designating the cell’s target size.

scholarly journals Multiple inputs ensure yeast cell size homeostasis during cell cycle progression

2017 ◽  
Author(s):  
Cecilia Garmendia-Torres ◽  
Olivier Tassy ◽  
Audrey Matifas ◽  
Nacho Molina ◽  
Gilles Charvin
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Cell Cycle Progression ◽  
Molecular Mechanisms ◽  
Cell Function ◽  
Size Control ◽  
Large Cell ◽  
Yeast Cells ◽  
Cycle Progression ◽  
Size Variability

AbstractCoordination of cell growth and division is essential for proper cell function. In budding yeast, although some molecular mechanisms responsible for cell size control during G1 have been elucidated, the mechanism by which cell size homeostasis is established and maintained throughout the cell cycle remains to be discovered. Here, we developed a new technique based on quantification of histone levels to monitor cell cycle progression in individual yeast cells with unprecedented accuracy. Our analysis establishes the existence of a strong mechanism controlling bud size in G2/M that prevents premature entry into mitosis, and contributes significantly to the overall control of size variability during the cell cycle. While most G1/S regulation mutants do not display any strongly impaired size homeostasis, mutants in which B-type cyclin regulation is altered display large cell-to-cell size variability. Our study thus demonstrates that size homeostasis is not controlled by a G1-specific mechanism but is likely to be an emergent property resulting from the integration of several mechanisms, including the control of cyclin B-Cdk activity, that coordinate cell and bud growth with division.

scholarly journals Cell size sensing in animal cells coordinates anabolic growth rates with cell cycle progression to maintain uniformity of cell size

2017 ◽  
Author(s):  
Miriam B. Ginzberg ◽  
Nancy Chang ◽  
Ran Kafri ◽  
Marc W. Kirschner
Keyword(s):  
Cell Cycle ◽  
Growth Rate ◽  
Cell Size ◽  
Growth Rates ◽  
Cell Cycle Progression ◽  
Time Lapse ◽  
Small Cells ◽  
Live Cells ◽  
Control Mechanisms ◽  
Animal Cells

AbstractThe uniformity of cell size in healthy tissues suggests that control mechanisms might coordinate cell growth and division. We derived a method to assay whether growth rates of individual cells depend on cell size, by combining time-lapse microscopy and immunofluorescence to monitor how variance in cell size changes as cells grow. This analysis revealed two periods in the cell cycle when cell size variance decreases in a manner incompatible with unregulated growth, suggesting that cells sense their own size and adjust their growth rate to correct aberrations. Monitoring nuclear growth in live cells confirmed that these decreases in variance reflect a process that selectively inhibits the growth of large cells while accelerating growth of small cells. We also detected cell-size-dependent adjustments of G1 length, which further reduce variability. Combining our assays with chemical and genetic perturbations confirmed that cells employ two strategies, adjusting both cell cycle length and growth rate, to maintain the appropriate size.

scholarly journals A conserved Lkb1 signaling axis modulates TORC2 signaling in budding yeast

2018 ◽  
Author(s):  
Maria Alcaide-Gavilán ◽  
Rafael Lucena ◽  
Katherine Schubert ◽  
Karen Artiles ◽  
Jessica Zapata ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Growth Rate ◽  
Cell Growth ◽  
Carbon Source ◽  
Cell Size ◽  
Nutrient Availability ◽  
Cell Cycle Progression ◽  
Budding Yeast ◽  
Small Cells ◽  
Cycle Progression

ABSTRACTNutrient availability, growth rate and cell size are closely linked. For example, in budding yeast, the rate of cell growth is proportional to nutrient availability, cell size is proportional to growth rate, and growth rate is proportional to cell size. Thus, cells grow slowly in poor nutrients and are nearly half the size of cells growing in rich nutrients. Moreover, large cells grow faster than small cells. A signaling network that surrounds Tor kinase complex 2 (TORC2) plays an important role in enforcing these proportional relationships. Cells that lack components of the TORC2 network fail to modulate their growth rate or size in response to changes in nutrient availability. Here, we show that budding yeast homologs of the Lkb1 tumor suppressor kinase are required for normal modulation of TORC2 signaling and in response to changes in carbon source. Lkb1 kinases activate Snf1/AMPK to initiate transcription of genes required for utilization of poor carbon sources. However, Lkb1 influences TORC2 signaling via a novel pathway that is independent of Snf1/AMPK. Of the three Lkb1 homologs in budding yeast, Elm1 plays the most important role in modulating TORC2. Elm1 activates a pair of related kinases called Gin4 and Hsl1. Previous work found that loss of Gin4 and Hsl1 causes cells to undergo unrestrained growth during a prolonged mitotic arrest, which suggests that play a role in linking cell cycle progression to cell growth. We found that Gin4 and Hsl1 also control the TORC2 network. In addition, Gin4 and Hsl1 are themselves influenced by signals from the TORC2 network, consistent with previous work showing that the TORC2 network constitutes a feedback loop. Together, the data suggest a model in which the TORC2 network sets growth rate in response to carbon source, while also relaying signals via Gin4 and Hsl1 that set the critical amount of growth required for cell cycle progression. This kind of close linkage between control of cell growth and size would suggest a simple mechanistic explanation for the proportional relationship between cell size and growth rate.

scholarly journals Multiple inputs ensure yeast cell size homeostasis during cell cycle progression

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Cecilia Garmendia-Torres ◽  
Olivier Tassy ◽  
Audrey Matifas ◽  
Nacho Molina ◽  
Gilles Charvin
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Cell Cycle Progression ◽  
Molecular Mechanisms ◽  
Cell Function ◽  
Size Control ◽  
Cycle Progression ◽  
Bud Size ◽  
Size Variability ◽  
A New Technique

Coordination of cell growth with division is essential for proper cell function. In budding yeast, although some molecular mechanisms responsible for cell size control during G1 have been elucidated, the mechanism by which cell size homeostasis is established remains to be discovered. Here, we developed a new technique based on quantification of histone levels to monitor cell cycle progression in individual cells with unprecedented accuracy. Our analysis establishes the existence of a mechanism controlling bud size in G2/M that prevents premature onset of anaphase, and controls the overall size variability. While most G1 mutants do not display impaired size homeostasis, mutants in which cyclin B-Cdk regulation is altered display large size variability. Our study thus demonstrates that size homeostasis is not controlled by a G1-specific mechanism alone but is likely to be an emergent property resulting from the integration of several mechanisms that coordinate cell and bud growth with division.

scholarly journals Dilution and titration of cell-cycle regulators may control cell size in budding yeast

2018 ◽  
Author(s):  
Frank S. Heldt ◽  
Reece Lunstone ◽  
John J. Tyson ◽  
Béla Novák
Keyword(s):  
Cell Cycle ◽  
Cell Growth ◽  
Cell Size ◽  
Cell Cycle Progression ◽  
Budding Yeast ◽  
Control Cell ◽  
Gene Copy Number ◽  
Size Control ◽  
Gene Copy ◽  
Cell Cycle Regulators

AbstractThe 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.

scholarly journals The Saccharomyces cerevisiae Anaphase-Promoting Complex Interacts with Multiple Histone-Modifying Enzymes To Regulate Cell Cycle Progression

2010 ◽  
Vol 9 (10) ◽  
pp. 1418-1431 ◽  
Author(s):  
Emma L. Turner ◽  
Mackenzie E. Malo ◽  
Marnie G. Pisclevich ◽  
Megan D. Dash ◽  
Gerald F. Davies ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Chromatin Assembly ◽  
Temperature Sensitive ◽  
Anaphase Promoting Complex ◽  
Cycle Progression ◽  
Ubiquitin Ligase Complex ◽  
Genes Encoding ◽  
Dependent Cell ◽  
Histone Modifying Enzymes

ABSTRACT The anaphase-promoting complex (APC), a large evolutionarily conserved ubiquitin ligase complex, regulates cell cycle progression through mitosis and G1. Here, we present data suggesting that APC-dependent cell cycle progression relies on a specific set of posttranslational histone-modifying enzymes. Multiple APC subunit mutants were impaired in total and modified histone H3 protein content. Acetylated H3K56 (H3K56Ac) levels were as reduced as those of total H3, indicating that loading histones with H3K56Ac is unaffected in APC mutants. However, under restrictive conditions, H3K9Ac and dimethylated H3K79 (H3K79me2) levels were more greatly reduced than those of total H3. In a screen for histone acetyltransferase (HAT) and histone deacetylase (HDAC) mutants that genetically interact with the apc5 CA (chromatin assembly) mutant, we found that deletion of GCN5 or ELP3 severely hampered apc5 CA temperature-sensitive (ts) growth. Further analyses showed that (i) the elp3Δ gcn5Δ double mutant ts defect was epistatic to that observed in apc5 CA cells; (ii) gcn5Δ and elp3Δ mutants accumulate in mitosis; and (iii) turnover of the APC substrate Clb2 is not impaired in elp3Δ gcn5Δ cells. Increased expression of ELP3 and GCN5, as well as genes encoding the HAT Rtt109 and the chromatin assembly factors Msi1 and Asf1, suppressed apc5 CA defects, while increased APC5 expression partially suppressed elp3Δ gcn5Δ growth defects. Finally, we demonstrate that Gcn5 is unstable during G1 and following G1 arrest and is stabilized in APC mutants. We present our working model in which Elp3/Gcn5 and the APC work together to facilitate passage through mitosis and G1. To progress into S, we propose that at least Gcn5 must then be targeted for degradation in an APC-dependent fashion.

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