Variability in individual cell cycles of Saccharomyces cerevisiae

1981 ◽  
Vol 50 (1) ◽  
pp. 361-376 ◽  
Author(s):  
P.G. Lord ◽  
A.E. Wheals
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Proliferation ◽  
Cell Size ◽  
Cycle Time ◽  
Cell Separation ◽  
Deterministic Model ◽  
Time Lapse ◽  
Nuclear Migration ◽  
Daughter Cells ◽  
Bud Emergence

The kinetics of cell proliferation of Saccharomyces cerevisiae were studied at 4 growth rates using time-lapse cinephotomicrography. Cells were grown on media with a high refractive index to reveal greater intracellular detail under the phase-contrast microscope. The morphological cell-cycle events scored were: bud emergence, nuclear migration, nuclear division, onset of cytokinesis and cell separation. Cell size was measured at cell separation and at bud emergence. The daughter-cycle time was always longer than the parent-cycle time mainly due to the large difference in the lengths of the unbudded phases. Parent cells had a shorter budded period than daughter cells. The large variance in daughter-cycle times was accounted for by the large variance in the lengths of the unbudded phase of daughter cells. The duration and variability of the periods in the cyclc from nuclear migration onwards were equivalent for parent and daughter cells. Daughter cells were always smaller than parent cells at division. There was wide variation in cell size at both division and bud emergence. The results indicated that a modified deterministic model could best explain cell proliferation kinetics in yeast. The data were used to evaluate 2 different models. The ‘sloppy size control’ model of Wheals (1981 a) was more consistent with the data than the ‘tandem’ model of Shilo, Shilo & Simchen (1976). The distribution of unbudded periods of daughter cells suggested that there was an additional incompressible period not present in parent cells.

scholarly journals Size control models of Saccharomyces cerevisiae cell proliferation.

1982 ◽  
Vol 2 (4) ◽  
pp. 361-368 ◽  
Author(s):  
A E Wheals
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Proliferation ◽  
Critical Size ◽  
Transition Probability ◽  
Size Control ◽  
Time Lapse ◽  
Growth Conditions ◽  
Yeast Cells ◽  
Cycle Times ◽  
The Individual

By using time-lapse photomicroscopy, the individual cycle times and sizes at bud emergence were measured for a population of saccharomyces cerevisiae cells growing exponentially under balanced growth conditions in a specially constructed filming slide. There was extensive variability in both parameters for daughter and parent cells. The data on 162 pairs of siblings were analyzed for agreement with the predictions of the transition probability hypothesis and the critical-size hypothesis of yeast cell proliferation and also with a model incorporating both of these hypotheses in tandem. None of the models accounted for all of the experimental data, but two models did give good agreement to all of the data. The wobbly tandem model proposes that cells need to attain a critical size, which is very variable, enabling them to enter a start state from which they exit with first order kinetics. The sloppy size control model suggests that cells have an increasing probability per unit time of traversing start as they increase in size, reaching a high plateau value which is less than one. Both models predict that the kinetics of entry into the cell division sequence will strongly depend on variability in birth size and thus will be quite different for daughters and parents of the asymmetrically dividing yeast cells. Mechanisms underlying these models are discussed.

scholarly journals Rate of cell cycle initiation of yeast cells when cell size is not a rate-determining factor

1983 ◽  
Vol 59 (1) ◽  
pp. 183-201 ◽  
Author(s):  
P.G. Lord ◽  
A.E. Wheals
Keyword(s):  
Cell Cycle ◽  
Steady State ◽  
Cell Size ◽  
Cycle Time ◽  
Yeast Cells ◽  
Size Difference ◽  
Birth Size ◽  
Daughter Cells ◽  
Alpha Factor ◽  
Determining Factor

The control of cell proliferation under steady-state conditions in the budding yeast, Saccharomyces cerevisiae, is well described by either the tandem or sloppy size control models, both of which suggest that differences in cycle time between individual cells or between parents and daughters is largely due to differences in birth size. These models have been investigated further under conditions in which cell size has not been a rate-determining factor for cell cycle initiation. Two approaches have been used. The first involves the growth of cells in low concentrations of hydroxyurea (HU), which has the effect of prolonging the duration of DNA synthesis. This leads to a lengthening of the budded period, which in turn leads to daughter cells being larger at division than the normal cell cycle initiation size of daughters in steady-state populations. The second approach involves the accumulation of cells at the key control point of the cycle, called start, using the pheromone alpha-factor. Since growth is unaffected, all cells eventually become larger than the volume at which they would normally initiate the cell cycle. The kinetics of proliferation were followed after release from alpha-factor arrest. The results from both approaches were broadly consistent with the predictions of both models. However, abolition of birth-size differences between parents and daughters in the presence of HU did not lead to a complete disappearance of differences in either cycle time or proliferation kinetics. Furthermore, following release from alpha-factor arrest, the rate of cell cycle initiation of parent cells was slower than in steady-state culture and the daughters' cells behaved as if comprising two separate populations. These discrepancies suggest that besides a size difference, there are additional physiological differences between parent and daughter cells.

scholarly journals A cell sizer network involving Cln3 and Far1 controls entrance into S phase in the mitotic cycle of budding yeast

2004 ◽  
Vol 167 (3) ◽  
pp. 433-443 ◽  
Author(s):  
Lilia Alberghina ◽  
Riccardo L. Rossi ◽  
Lorenzo Querin ◽  
Valeria Wanke ◽  
Marco Vanoni
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Replication ◽  
Carbon Source ◽  
Protein Content ◽  
Cell Size ◽  
Mitotic Cycle ◽  
S Phase ◽  
Wild Type ◽  
Bud Emergence ◽  
A Cell

Saccharomyces cerevisiae must reach a carbon source-modulated critical cell size, protein content per cell at the onset of DNA replication (Ps), in order to enter S phase. Cells grown in glucose are larger than cells grown in ethanol. Here, we show that an increased level of the cyclin-dependent inhibitor Far1 increases cell size, whereas far1Δ cells start bud emergence and DNA replication at a smaller size than wild type. Cln3Δ, far1Δ, and strains overexpressing Far1 do not delay budding during an ethanol glucose shift-up as wild type does. Together, these findings indicate that Cln3 has to overcome Far1 to trigger Cln–Cdc28 activation, which then turns on SBF- and MBF-dependent transcription. We show that a second threshold is required together with the Cln3/Far1 threshold for carbon source modulation of Ps. A new molecular network accounting for the setting of Ps is proposed.

scholarly journals Symmetric cell division in pseudohyphae of the yeast Saccharomyces cerevisiae.

1994 ◽  
Vol 5 (9) ◽  
pp. 1003-1022 ◽  
Author(s):  
S J Kron ◽  
C A Styles ◽  
G R Fink
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Cell Size ◽  
Time Lapse ◽  
Cell Types ◽  
Yeast Saccharomyces Cerevisiae ◽  
Distinct Cell ◽  
Mother And Daughter ◽  
Dividing Cells ◽  
Unique Cell

Laboratory strains of Saccharomyces cerevisiae are dimorphic; in response to nitrogen starvation they switch from a yeast form (YF) to a filamentous pseudohyphal (PH) form. Time-lapse video microscopy of dividing cells reveals that YF and PH cells differ in their cell cycles and budding polarity. The YF cell cycle is controlled at the G1/S transition by the cell-size checkpoint Start. YF cells divide asymmetrically, producing small daughters from full-sized mothers. As a result, mothers and daughters bud asynchronously. Mothers bud immediately but daughters grow in G1 until they achieve a critical cell size. By contrast, PH cells divide symmetrically, restricting mitosis until the bud grows to the size of the mother. Thus, mother and daughter bud synchronously in the next cycle, without a G1 delay before Start. YF and PH cells also exhibit distinct bud-site selection patterns. YF cells are bipolar, producing their second and subsequent buds at either pole. PH cells are unipolar, producing their second and subsequent buds only from the end opposite the junction with their mother. We propose that in PH cells a G2 cell-size checkpoint delays mitosis until bud size reaches that of the mother cell. We conclude that yeast and PH forms are distinct cell types each with a unique cell cycle, budding pattern, and cell shape.

scholarly journals Cell cycle phase expansion in nitrogen-limited cultures of Saccharomyces cerevisiae.

1980 ◽  
Vol 85 (1) ◽  
pp. 96-107 ◽  
Author(s):  
C J Rivin ◽  
W L Fangman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Cycle Length ◽  
Time Lapse ◽  
S Phase ◽  
Cycle Phase ◽  
Yeast Saccharomyces Cerevisiae ◽  
Bud Emergence ◽  
Length Changes ◽  
Cell Cycle Length

The time and coordination of cell cycle events were examined in the budding yeast Saccharomyces cerevisiae. Whole-cell autoradiographic techniques and time-lapse photography were used to measure the duration of the S, G1, and G2 phases, and the cell cycle positions of "start" and bud emergence, in cells whose growth rates were determined by the source of nitrogen. It was observed that the G1, S, and G2 phases underwent a proportional expansion with increasing cell cycle length, with the S phase occupying the middle half of the cell cycle. In each growth condition, start appeared to correspond to the G1 phase/S phase boundary. Bud emergence did not occur until mid S phase. These results show that the rate of transit through all phases of the cell cycle can vary considerably when cell cycle length changes. When cells growing at different rates were arrested in G1, the following synchronous S phase were of the duration expected from the length of S in each asynchronous population. Cells transferred from a poor nitrogen source to a good one after arrest in G1 went through the subsequent S phase at a rate characteristic of the better medium, indicating that cells are not committed in G1 to an S phase of a particular duration.

scholarly journals Involvement of an Actomyosin Contractile Ring in Saccharomyces cerevisiae Cytokinesis

1998 ◽  
Vol 142 (5) ◽  
pp. 1301-1312 ◽  
Author(s):  
Erfei Bi ◽  
Paul Maddox ◽  
Daniel J. Lew ◽  
E.D. Salmon ◽  
John N. McMillan ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Separation ◽  
Cortical Actin ◽  
Primary Defect ◽  
Septum Formation ◽  
Bud Emergence ◽  
Bud Neck ◽  
Bud Site ◽  
Type Ii Myosin

In Saccharomyces cerevisiae, the mother cell and bud are connected by a narrow neck. The mechanism by which this neck is closed during cytokinesis has been unclear. Here we report on the role of a contractile actomyosin ring in this process. Myo1p (the only type II myosin in S. cerevisiae) forms a ring at the presumptive bud site shortly before bud emergence. Myo1p ring formation depends on the septins but not on F-actin, and preexisting Myo1p rings are stable when F-actin is depolymerized. The Myo1p ring remains in the mother–bud neck until the end of anaphase, when a ring of F-actin forms in association with it. The actomyosin ring then contracts to a point and disappears. In the absence of F-actin, the Myo1p ring does not contract. After ring contraction, cortical actin patches congregate at the mother–bud neck, and septum formation and cell separation rapidly ensue. Strains deleted for MYO1 are viable; they fail to form the actin ring but show apparently normal congregation of actin patches at the neck. Some myo1Δ strains divide nearly as efficiently as wild type; other myo1Δ strains divide less efficiently, but it is unclear whether the primary defect is in cytokinesis, septum formation, or cell separation. Even cells lacking F-actin can divide, although in this case division is considerably delayed. Thus, the contractile actomyosin ring is not essential for cytokinesis in S. cerevisiae. In its absence, cytokinesis can still be completed by a process (possibly localized cell–wall synthesis leading to septum formation) that appears to require septin function and to be facilitated by F-actin.

scholarly journals Constriction rate modulation can drive cell size control and homeostasis inC. crescentus

2018 ◽  
Author(s):  
Ambroise Lambert ◽  
Aster Vanhecke ◽  
Anna Archetti ◽  
Seamus Holden ◽  
Felix Schaber ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Caulobacter Crescentus ◽  
Size Control ◽  
Time Lapse ◽  
Structured Illumination ◽  
Structured Illumination Microscopy ◽  
Daughter Cells ◽  
Division Site ◽  
Cell Size Control

AbstractRod-shaped bacteria typically grow first via sporadic and dispersed elongation along their lateral walls, then via a combination of zonal elongation and constriction at the division site to form the poles of daughter cells. Although constriction comprises up to half of the cell cycle, its impact on cell size control and homeostasis has rarely been considered. To reveal the roles of cell elongation and constriction in bacterial size regulation during cell division, we captured the shape dynamics ofCaulobacter crescentuswith time-lapse structured illumination microscopy and used molecular markers as cell-cycle landmarks. We perturbed constriction rate using a hyperconstriction mutant or fosfomycin inhibition. We report that constriction rate contributes to both size control and homeostasis, by determining elongation during constriction, and by compensating for variation in pre-constriction elongation on a single-cell basis.

scholarly journals The Sle1 Cell Wall Amidase Controls Daughter Cell Splitting, Cell Size, and β-Lactam Resistance in Community Acquired Methicillin Resistant Staphylococcus aureus USA300

2019 ◽  
Author(s):  
Ida Thalsø-Madsen ◽  
Fernando Ruiz Torrubia ◽  
Lijuan Xu ◽  
Andreas Petersen ◽  
Camilla Jensen ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Cell Wall ◽  
Cell Size ◽  
Cell Separation ◽  
Methicillin Resistant ◽  
Daughter Cells ◽  
Fast Spreading ◽  
A Cell ◽  
Usa300 Clone ◽  
Highly Virulent

SummaryMost clinically relevant methicillin resistant Staphylococcus aureus (MRSA) strains have become resistant to β-lactams antibiotics through horizontal acquisition of the mecA gene encoding PBP2a, a peptidoglycan transpeptidase with low affinity for β-lactams. The level of resistance conferred by mecA is, however, strain dependent and the mechanisms underlying this phenomenon remain poorly understood. We here show that β-lactam resistance correlates to expression of the Sle1 cell wall amidase in the fast spreading and highly virulent community-acquired MRSA USA300 clone. Sle1 is a substrate of the ClpXP protease, and while the high Sle1 levels in cells lacking ClpXP activity confer β-lactam hyper-resistance, USA300 cells lacking Sle1 are as sensitive to β-lactams as cells lacking mecA. This finding prompted us to assess the cellular roles of Sle1 in more detail, and we demonstrate that high Sle1 levels accelerate the onset of daughter cells splitting and decrease cell size. Vice versa, oxacillin decreases the Sle1 level, and imposes a cell-separation defect that is antagonized by high Sle1 levels, suggesting that high Sle1 levels increase tolerance to oxacillin by promoting cell separation. In contrast, increased oxacillin sensitivity of sle1 cells appears linked to a synthetical lethal effect on septum synthesis. In conclusion, this study demonstrates that Sle1 is a key factor in resistance to β-lactam antibiotics in the JE2 USA300 model strain, and that PBP2a is required for expression of Sle1 in JE2 cells exposed to oxacillin.ImportanceThe bacterium Staphylococcus aureus is a major cause of human disease, and the global spread of S. aureus resistant to β-lactam antibiotics (MRSA) has made treatment increasingly difficult. β-lactams interfere with cross-linking of the bacterial cell wall, however, the killing mechanism of this important class of antibiotics is still not fully understood. Here we provide novel insight into this topic by showing that β-lactam resistance is controlled by the Sle1 cell wall amidase in the fast spreading and highly virulent MRSA USA300 clone. We show that Sle1 high levels accelerate the onset of daughter cells splitting and decrease cell size. Vice versa, oxacillin decreases the Sle1 level, and imposes a cell-separation defect that is antagonized Sle1. The key finding that resistance to β-lactams correlates positively to expression of Sle1 indicates that, in S. aureus, the detrimental effects of β-lactam antibiotics are linked to inhibition of daughter cells splitting.

scholarly journals Patterns of bud-site selection in the yeast Saccharomyces cerevisiae.

1995 ◽  
Vol 129 (3) ◽  
pp. 751-765 ◽  
Author(s):  
J Chant ◽  
J R Pringle
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Time Lapse ◽  
Growth Conditions ◽  
Alpha Cells ◽  
Yeast Saccharomyces Cerevisiae ◽  
Cell Cycles ◽  
Daughter Cells ◽  
Division Site ◽  
Mother Cells ◽  
Bud Site

Cells of the yeast Saccharomyces cerevisiae select bud sites in either of two distinct spatial patterns, known as axial (expressed by a and alpha cells) and bipolar (expressed by a/alpha cells). Fluorescence, time-lapse, and scanning electron microscopy have been used to obtain more precise descriptions of these patterns. From these descriptions, we conclude that in the axial pattern, the new bud forms directly adjacent to the division site in daughter cells and directly adjacent to the immediately preceding division site (bud site) in mother cells, with little influence from earlier sites. Thus, the division site appears to be marked by a spatial signal(s) that specifies the location of the new bud site and is transient in that it only lasts from one budding event to the next. Consistent with this conclusion, starvation and refeeding of axially budding cells results in the formation of new buds at nonaxial sites. In contrast, in bipolar budding cells, both poles are specified persistently as potential bud sites, as shown by the observations that a pole remains competent for budding even after several generations of nonuse and that the poles continue to be used for budding after starvation and refeeding. It appears that the specification of the two poles as potential bud sites occurs before a daughter cell forms its first bud, as a daughter can form this bud near either pole. However, there is a bias towards use of the pole distal to the division site. The strength of this bias varies from strain to strain, is affected by growth conditions, and diminishes in successive cell cycles. The first bud that forms near the distal pole appears to form at the very tip of the cell, whereas the first bud that forms near the pole proximal to the original division site (as marked by the birth scar) is generally somewhat offset from the tip and adjacent to (or overlapping) the birth scar. Subsequent buds can form near either pole and appear almost always to be adjacent either to the birth scar or to a previous bud site. These observations suggest that the distal tip of the cell and each division site carry persistent signals that can direct the selection of a bud site in any subsequent cell cycle.

Size control models of Saccharomyces cerevisiae cell proliferation

1982 ◽  
Vol 2 (4) ◽  
pp. 361-368
Author(s):  
A E Wheals
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Proliferation ◽  
Critical Size ◽  
Transition Probability ◽  
Size Control ◽  
Time Lapse ◽  
Growth Conditions ◽  
Yeast Cells ◽  
Cycle Times ◽  
The Individual

By using time-lapse photomicroscopy, the individual cycle times and sizes at bud emergence were measured for a population of saccharomyces cerevisiae cells growing exponentially under balanced growth conditions in a specially constructed filming slide. There was extensive variability in both parameters for daughter and parent cells. The data on 162 pairs of siblings were analyzed for agreement with the predictions of the transition probability hypothesis and the critical-size hypothesis of yeast cell proliferation and also with a model incorporating both of these hypotheses in tandem. None of the models accounted for all of the experimental data, but two models did give good agreement to all of the data. The wobbly tandem model proposes that cells need to attain a critical size, which is very variable, enabling them to enter a start state from which they exit with first order kinetics. The sloppy size control model suggests that cells have an increasing probability per unit time of traversing start as they increase in size, reaching a high plateau value which is less than one. Both models predict that the kinetics of entry into the cell division sequence will strongly depend on variability in birth size and thus will be quite different for daughters and parents of the asymmetrically dividing yeast cells. Mechanisms underlying these models are discussed.

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