scholarly journals F-actin distribution and function during sexual differentiation in Schizosaccharomyces pombe

1998 ◽  
Vol 111 (7) ◽  
pp. 867-876 ◽  
Author(s):  
J. Petersen ◽  
O. Nielsen ◽  
R. Egel ◽  
I.M. Hagan
Keyword(s):  
Cell Cycle ◽  
Schizosaccharomyces Pombe ◽  
Cell Fusion ◽  
Sexual Differentiation ◽  
Nitrogen Starvation ◽  
Spindle Pole ◽  
Actin Binding ◽  
G1 Phase ◽  
Latrunculin A ◽  
Meiosis I

Sexual differentiation in Schizosaccharomyces pombe is induced from the G1 phase of the cell cycle by nitrogen starvation and the presence of mating pheromones. We describe the distribution of F-actin during sexual differentiation. Cortical F-actin dots have previously been shown to be restricted to one end of the rod shaped cell during the G1 phase of the cell cycle. Within half an hour of nitrogen starvation the distribution of cortical F-actin dots switched from being monopolar to bipolar. This was then reversed as the F-actin cytoskeleton repolarized so that cortical F-actin dots accumulated towards the projection tip at one end of the cell. Following cell fusion, F-actin dots were randomly scattered during the horsetail movement that precedes meiosis I and remained scattered until prometaphase or metaphase of meiosis II, when they concentrated around the nucleus. F-actin was seen on the lagging face of the nuclei which faced the partner nucleus during anaphase B of meiosis II. Early on in this anaphase F-actin was also seen on the opposite side of the nucleus, near the spindle pole body. F-actin accumulated within the spores in the mature ascus. Treatment with the actin depolymerising drug Latrunculin A showed that F-actin is required for cell fusion and spore formation. Latrunculin A treatment extended all stages from karyogamy to meiosis I. The S. pombe homologue of the actin binding protein profilin, Cdc3, was shown to be required for conjugation. Cdc3 co-localized with the formin related molecule Fus1 at the projection tip. The polarization of F-actin cortical dots to the projection tip was unaffected in the cdc3.124 mutant, but cdc3.124 mutant cells were unable to break down the cell walls between the two cells following agglutination.

Regulation of the start of DNA replication in Schizosaccharomyces pombe

1999 ◽  
Vol 112 (6) ◽  
pp. 939-946 ◽  
Author(s):  
C.R. Carlson ◽  
B. Grallert ◽  
T. Stokke ◽  
E. Boye
Keyword(s):  
Cell Cycle ◽  
Flow Cytometry ◽  
Growth Rate ◽  
Schizosaccharomyces Pombe ◽  
Growth Rates ◽  
Cell Separation ◽  
Cell Mass ◽  
Nitrogen Sources ◽  
S Phase ◽  
G1 Phase

Cells of Schizosaccharomyces pombe were grown in minimal medium with different nitrogen sources under steady-state conditions, with doubling times ranging from 2.5 to 14 hours. Flow cytometry and fluorescence microscopy confirmed earlier findings that at rapid growth rates, the G1 phase was short and cell separation occurred at the end of S phase. For some nitrogen sources, the growth rate was greatly decreased, the G1 phase occupied 30–50% of the cell cycle, and cell separation occurred in early G1. In contrast, other nitrogen sources supported low growth rates without any significant increase in G1 duration. The method described allows manipulation of the length of G1 and the relative cell cycle position of S phase in wild-type cells. Cell mass was measured by flow cytometry as scattered light and as protein-associated fluorescence. The extensions of G1 were not related to cell mass at entry into S phase. Our data do not support the hypothesis that the cells must reach a certain fixed, critical mass before entry into S. We suggest that cell mass at the G1/S transition point is variable and determined by a set of molecular parameters. In the present experiments, these parameters were influenced by the different nitrogen sources in a way that was independent of the actual growth rate.

scholarly journals Cdc14 phosphatase directs centrosome re-duplication at the meiosis I to meiosis II transition in budding yeast

2017 ◽  
Vol 2 ◽  
pp. 2 ◽  
Author(s):  
Colette Fox ◽  
Juan Zou ◽  
Juri Rappsilber ◽  
Adele L. Marston
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Chromosome Segregation ◽  
Budding Yeast ◽  
Spindle Pole Body ◽  
Initial Step ◽  
Mitotic Cell ◽  
Spindle Pole ◽  
Fluorescence And Electron Microscopy ◽  
Meiosis I

Background Gametes are generated through a specialized cell division called meiosis, in which ploidy is reduced by half because two consecutive rounds of chromosome segregation, meiosis I and meiosis II, occur without intervening DNA replication. This contrasts with the mitotic cell cycle where DNA replication and chromosome segregation alternate to maintain the same ploidy. At the end of mitosis, CDKs are inactivated. This low CDK state in late mitosis/G1 allows for critical preparatory events for DNA replication and centrosome/spindle pole body (SPB) duplication. However, their execution is inhibited until S phase, where further preparatory events are also prevented. This “licensing” ensures that both the chromosomes and the centrosomes/SPBs replicate exactly once per cell cycle, thereby maintaining constant ploidy. Crucially, between meiosis I and meiosis II, centrosomes/SPBs must be re-licensed, but DNA re-replication must be avoided. In budding yeast, the Cdc14 protein phosphatase triggers CDK down regulation to promote exit from mitosis. Cdc14 also regulates the meiosis I to meiosis II transition, though its mode of action has remained unclear. Methods Fluorescence and electron microscopy was combined with proteomics to probe SPB duplication in cells with inactive or hyperactive Cdc14. Results We demonstrate that Cdc14 ensures two successive nuclear divisions by re-licensing SPBs at the meiosis I to meiosis II transition. We show that Cdc14 is asymmetrically enriched on a single SPB during anaphase I and provide evidence that this enrichment promotes SPB re-duplication. Cells with impaired Cdc14 activity fail to promote extension of the SPB half-bridge, the initial step in morphogenesis of a new SPB. Conversely, cells with hyper-active Cdc14 duplicate SPBs, but fail to induce their separation. Conclusion Our findings implicate reversal of key CDK-dependent phosphorylations in the differential licensing of cyclical events at the meiosis I to meiosis I transition.

The Effect of 2-Phenyl Ethanol on the DNA Synthesis Cycle of Schizosaccharomyces Pombe

1970 ◽  
Vol 7 (2) ◽  
pp. 523-530
Author(s):  
C. J. BOSTOCK
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Schizosaccharomyces Pombe ◽  
Normal Growth ◽  
S Phase ◽  
G1 Phase ◽  
Synchronous Cultures ◽  
Number Of Cells

The effect of different concentrations of 2-phenyl ethanol (PE) on growth and DNA synthesis of Schizosaccharomyces pombe is described. o.3% PE inhibits the entry of cells into S phase, but allows a doubling in the number of cells in the culture. The effect of o.2% PE on random and synchronous cultures of S. pombe shows that, in the continued presence of the inhibitor, the S phase is moved to a different point in the cell cycle. Cells continue to grow in the presence of o.2% PE with a G1 phase occupying a significant portion of the cell cycle. This differs from normal growth when the G1 phase is absent.

scholarly journals Control of the mitotic exit network during meiosis

2012 ◽  
Vol 23 (16) ◽  
pp. 3122-3132 ◽  
Author(s):  
Michelle A. Attner ◽  
Angelika Amon
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Signaling Pathway ◽  
Vegetative Growth ◽  
Spindle Pole ◽  
Mitotic Exit ◽  
Regulatory Pathways ◽  
Spindle Pole Bodies ◽  
Mitotic Exit Network ◽  
Meiosis I

The mitotic exit network (MEN) is an essential GTPase signaling pathway that triggers exit from mitosis in budding yeast. We show here that during meiosis, the MEN is dispensable for exit from meiosis I but contributes to the timely exit from meiosis II. Consistent with a role for the MEN during meiosis II, we find that the signaling pathway is active only during meiosis II. Our analysis further shows that MEN signaling is modulated during meiosis in several key ways. Whereas binding of MEN components to spindle pole bodies (SPBs) is necessary for MEN signaling during mitosis, during meiosis MEN signaling occurs off SPBs and does not require the SPB recruitment factor Nud1. Furthermore, unlike during mitosis, MEN signaling is controlled through the regulated interaction between the MEN kinase Dbf20 and its activating subunit Mob1. Our data lead to the conclusion that a pathway essential for vegetative growth is largely dispensable for the specialized meiotic divisions and provide insights into how cell cycle regulatory pathways are modulated to accommodate different modes of cell division.

scholarly journals The Role of Topoisomerase II in Meiotic Chromosome Condensation and Segregation in Schizosaccharomyces pombe

1998 ◽  
Vol 9 (10) ◽  
pp. 2739-2750 ◽  
Author(s):  
Edgar Hartsuiker ◽  
Jürg Bähler ◽  
Jürg Kohli
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Topoisomerase Ii ◽  
Meiotic Chromosome ◽  
Chromatin Condensation ◽  
Spindle Pole ◽  
Primary Defect ◽  
Spindle Pole Bodies ◽  
Topological State ◽  
Meiosis I

Topoisomerase II is able to break and rejoin double-strand DNA. It controls the topological state and forms and resolves knots and catenanes. Not much is known about the relation between the chromosome segregation and condensation defects as found in yeasttop2 mutants and the role of topoisomerase II in meiosis. We studied meiosis in a heat-sensitive top2mutant of Schizosaccharomyces pombe. Topoisomerase II is not required until shortly before meiosis I. The enzyme is necessary for condensation shortly before the first meiotic division but not for early meiotic prophase condensation. DNA replication, prophase morphology, and dynamics of the linear elements are normal in thetop2 mutant. The top2 cells are not able to perform meiosis I. Arrested cells have four spindle pole bodies and two spindles but only one nucleus, suggesting that the arrest is nonregulatory. Finally, we show that the arrest is partly solved in atop2 rec7 double mutant, indicating that topoisomerase II functions in the segregation of recombined chromosomes. We suggest that the inability to decatenate the replicated DNA is the primary defect in top2. This leads to a loss of chromatin condensation shortly before meiosis I, failure of sister chromatid separation, and a nonregulatory arrest.

scholarly journals The S. pombe CDK5 ortholog Pef1 regulates sexual differentiation through control of the TORC1 pathway and autophagy

2020 ◽  
Vol 133 (17) ◽  
pp. jcs247817
Author(s):  
Shinya Matsuda ◽  
Ushio Kikkawa ◽  
Haruka Uda ◽  
Akio Nakashima
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Fission Yeast ◽  
Sexual Differentiation ◽  
Environmental Changes ◽  
Nitrogen Starvation ◽  
General Strategy ◽  
Positive Regulation ◽  
Starvation Response ◽  
Double Deletion ◽  
Early Phases

ABSTRACTIn Schizosaccharomyces pombe, a general strategy for survival in response to environmental changes is sexual differentiation, which is triggered by TORC1 inactivation. However, mechanisms of TORC1 regulation in fission yeast remain poorly understood. In this study, we found that Pef1, which is an ortholog of mammalian CDK5, regulates the initiation of sexual differentiation through positive regulation of TORC1 activity. Conversely, deletion of pef1 leads to activation of autophagy and subsequent excessive TORC1 reactivation during the early phases of the nitrogen starvation response. This excessive TORC1 reactivation results in the silencing of the Ste11-Mei2 pathway and mating defects. Additionally, we found that pef1 genetically interacts with tsc1 and tsc2 for TORC1 regulation, and physically interacts with three cyclins, Clg1, Pas1 and Psl1. The double deletion of clg1 and pas1 promotes activation of autophagy and TORC1 during nitrogen starvation, similar to what is seen in pef1Δ cells. Overall, our work suggests that Pef1–Clg1 and Pef1–Pas1 complexes regulate initiation of sexual differentiation through control of the TSC–TORC1 pathway and autophagy.

Complementation of G1-phase variants of a mammalian cell cycle

1979 ◽  
Vol 35 (1) ◽  
pp. 53-58
Author(s):  
P.M. Naha
Keyword(s):  
Cell Cycle ◽  
Cell Fusion ◽  
Mammalian Cell ◽  
S Phase ◽  
G1 Phase ◽  
Temperature Sensitive ◽  
Multinucleated Cells ◽  
Mammalian Cell Cycle ◽  
Complementation Groups ◽  
Phase Variants

Complementation between temperature-sensitive (ts) variants of Balb/c-3T3 defective in the G1 phase of its cell cycle was measured in the [3H]thymidine-labeling indices of the multinucleated cells during incubation at the restricted temperature (38 degrees C) following cell fusion. One ts variant from each group along the length of the G1 phase was tested for complementation. Varying degrees of complementation were observed between the 4 ts variants tested, judging by the time of entry into S-phase and the degree of synchrony attained. At least 3 complementation groups were discernible.

scholarly journals Cdc14 phosphatase directs centrosome re-duplication at the meiosis I to meiosis II transition in budding yeast

2017 ◽  
Vol 2 ◽  
pp. 2 ◽  
Author(s):  
Colette Fox ◽  
Juan Zou ◽  
Juri Rappsilber ◽  
Adele L. Marston
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Chromosome Segregation ◽  
Budding Yeast ◽  
Spindle Pole Body ◽  
Initial Step ◽  
Mitotic Cell ◽  
Spindle Pole ◽  
Fluorescence And Electron Microscopy ◽  
Meiosis I

Background: Gametes are generated through a specialized cell division called meiosis, in which ploidy is reduced by half because two consecutive rounds of chromosome segregation, meiosis I and meiosis II, occur without intervening DNA replication. This contrasts with the mitotic cell cycle where DNA replication and chromosome segregation alternate to maintain the same ploidy. At the end of mitosis, cyclin-dependent kinases (CDKs) are inactivated. This low CDK state in late mitosis/G1 allows for critical preparatory events for DNA replication and centrosome/spindle pole body (SPB) duplication. However, their execution is inhibited until S phase, where further preparatory events are also prevented. This “licensing” ensures that both the chromosomes and the centrosomes/SPBs replicate exactly once per cell cycle, thereby maintaining constant ploidy. Crucially, between meiosis I and meiosis II, centrosomes/SPBs must be re-licensed, but DNA re-replication must be avoided. In budding yeast, the Cdc14 protein phosphatase triggers CDK down regulation to promote exit from mitosis. Cdc14 also regulates the meiosis I to meiosis II transition, though its mode of action has remained unclear. Methods: Fluorescence and electron microscopy was combined with proteomics to probe SPB duplication in cells with inactive or hyperactive Cdc14. Results: We demonstrate that Cdc14 ensures two successive nuclear divisions by re-licensing SPBs at the meiosis I to meiosis II transition. We show that Cdc14 is asymmetrically enriched on a single SPB during anaphase I and provide evidence that this enrichment promotes SPB re-duplication. Cells with impaired Cdc14 activity fail to promote extension of the SPB half-bridge, the initial step in morphogenesis of a new SPB. Conversely, cells with hyper-active Cdc14 duplicate SPBs, but fail to induce their separation. Conclusion: Our findings implicate reversal of key CDK-dependent phosphorylations in the differential licensing of cyclical events at the meiosis I to meiosis II transition.

scholarly journals Microtubule Dynamics from Mating through the First Zygotic Division in the Budding Yeast Saccharomyces cerevisiae

1999 ◽  
Vol 144 (5) ◽  
pp. 977-987 ◽  
Author(s):  
Paul Maddox ◽  
E. Chin ◽  
A. Mallavarapu ◽  
E. Yeh ◽  
E.D. Salmon ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Cell Fusion ◽  
Fluorescent Protein ◽  
Budding Yeast ◽  
Time Lapse ◽  
Spindle Pole ◽  
Microtubule Dynamics ◽  
Cell Cycle Checkpoints ◽  
Yeast Saccharomyces Cerevisiae

We have used time-lapse digital imaging microscopy to examine cytoplasmic astral microtubules (Mts) and spindle dynamics during the mating pathway in budding yeast Saccharomyces cerevisiae. Mating begins when two cells of opposite mating type come into proximity. The cells arrest in the G1 phase of the cell cycle and grow a projection towards one another forming a shmoo projection. Imaging of microtubule dynamics with green fluorescent protein (GFP) fusions to dynein or tubulin revealed that the nucleus and spindle pole body (SPB) became oriented and tethered to the shmoo tip by a Mt-dependent search and capture mechanism. Dynamically unstable astral Mts were captured at the shmoo tip forming a bundle of three or four astral Mts. This bundle changed length as the tethered nucleus and SPB oscillated toward and away from the shmoo tip at growth and shortening velocities typical of free plus end astral Mts (∼0.5 μm/min). Fluorescent fiduciary marks in Mt bundles showed that Mt growth and shortening occurred primarily at the shmoo tip, not the SPB. This indicates that Mt plus end assembly/disassembly was coupled to pushing and pulling of the nucleus. Upon cell fusion, a fluorescent bar of Mts was formed between the two shmoo tip bundles, which slowly shortened (0.23 ± 0.07 μm/min) as the two nuclei and their SPBs came together and fused (karyogamy). Bud emergence occurred adjacent to the fused SPB ∼30 min after SPB fusion. During the first mitosis, the SPBs separated as the spindle elongated at a constant velocity (0.75 μm/min) into the zygotic bud. There was no indication of a temporal delay at the 2-μm stage of spindle morphogenesis or a lag in Mt nucleation by replicated SPBs as occurs in vegetative mitosis implying a lack of normal checkpoints. Thus, the shmoo tip appears to be a new model system for studying Mt plus end dynamic attachments and much like higher eukaryotes, the first mitosis after haploid cell fusion in budding yeast may forgo cell cycle checkpoints present in vegetative mitosis.

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