scholarly journals Hyphal Elongation Is Regulated Independently of Cell Cycle inCandida albicans

2002 ◽  
Vol 13 (1) ◽  
pp. 134-145 ◽  
Author(s):  
Idit Hazan ◽  
Marisa Sepulveda-Becerra ◽  
Haoping Liu
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Cell Morphogenesis ◽  
Hyphal Morphogenesis ◽  
Pole Body ◽  
Cycle Regulation ◽  
Germ Tubes ◽  
Incandida Albicans

The mechanism for apical growth during hyphal morphogenesis inCandida albicans is unknown. Studies fromSaccharomyces cerevisiae indicate that cell morphogenesis may involve cell cycle regulation by cyclin-dependent kinase. To examine whether this is the mechanism for hyphal morphogenesis, the temporal appearance of different spindle pole body and spindle structures, the cell cycle-regulated rearrangements of the actin cytoskeleton, and the phosphorylation state of the conserved Tyr19 of Cdc28 during the cell cycle were compared and found to be similar between yeast and serum-induced hyphal apical cells. These data suggest that hyphal elongation is not mediated by altering cell cycle progression or through phosphorylation of Tyr19 of Cdc28. We have also shown that germ tubes can evaginate before spindle pole body duplication, chitin ring formation, and DNA replication. Similarly, tip-associated actin polarization in each hypha occurs before the events of the G1/S transition and persists throughout the cell cycle, whereas cell cycle-regulated actin assemblies come and go. We have also shown that cells in phases other than G1can be induced to form hyphae. Hyphae induced from G1cells have no constrictions, and the first chitin ring is positioned in the germ tube at various distances from the base. Hyphae induced from budded cells have a constriction and a chitin ring at the bud neck, beyond which the hyphae continue to elongate with no further constrictions. Our data suggest that hyphal elongation and cell cycle morphogenesis programs are uncoupled, and each contributes to different aspects of cell morphogenesis.

scholarly journals A Proteasome Cap Subunit Required for Spindle Pole Body Duplication in Yeast

1997 ◽  
Vol 137 (3) ◽  
pp. 539-553 ◽  
Author(s):  
Heather B. McDonald ◽  
Breck Byers
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Fluorescent Protein ◽  
Sequence Similarity ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
Protein Fusion ◽  
Pole Body

Proteasome-mediated protein degradation is a key regulatory mechanism in a diversity of complex processes, including the control of cell cycle progression. The selection of substrates for degradation clearly depends on the specificity of ubiquitination mechanisms, but further regulation may occur within the proteasomal 19S cap complexes, which attach to the ends of the 20S proteolytic core and are thought to control entry of substrates into the core. We have characterized a gene from Saccharomyces cerevisiae that displays extensive sequence similarity to members of a family of ATPases that are components of the 19S complex, including human subunit p42 and S. cerevisiae SUG1/ CIM3 and CIM5 products. This gene, termed PCS1 (for proteasomal cap subunit), is identical to the recently described SUG2 gene (Russell, S.J., U.G. Sathyanarayana, and S.A. Johnston. 1996. J. Biol. Chem. 271:32810– 32817). We have shown that PCS1 function is essential for viability. A temperature-sensitive pcs1 strain arrests principally in the second cycle after transfer to the restrictive temperature, blocking as large-budded cells with a G2 content of unsegregated DNA. EM reveals that each arrested pcs1 cell has failed to duplicate its spindle pole body (SPB), which becomes enlarged as in other monopolar mutants. Additionally, we have shown localization of a functional Pcs1–green fluorescent protein fusion to the nucleus throughout the cell cycle. We hypothesize that Pcs1p plays a role in the degradation of certain potentially nuclear component(s) in a manner that specifically is required for SPB duplication.

scholarly journals Key phosphorylation events in Spc29 and Spc42 guide multiple steps of yeast centrosome duplication

2018 ◽  
Vol 29 (19) ◽  
pp. 2280-2291 ◽  
Author(s):  
Michele Haltiner Jones ◽  
Eileen T. O’Toole ◽  
Amy S. Fabritius ◽  
Eric G. Muller ◽  
Janet B. Meehl ◽  
...  
Keyword(s):  
Cell Cycle Progression ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Centrosome Duplication ◽  
Phosphorylation Sites ◽  
Cycle Progression ◽  
Cellular Processes ◽  
Pole Body ◽  
Core Components ◽  
Spindle Elongation

Phosphorylation modulates many cellular processes during cell cycle progression. The yeast centrosome (called the spindle pole body, SPB) is regulated by the protein kinases Mps1 and Cdc28/Cdk1 as it nucleates microtubules to separate chromosomes during mitosis. Previously we completed an SPB phosphoproteome, identifying 297 sites on 17 of the 18 SPB components. Here we describe mutagenic analysis of phosphorylation events on Spc29 and Spc42, two SPB core components that were shown in the phosphoproteome to be heavily phosphorylated. Mutagenesis at multiple sites in Spc29 and Spc42 suggests that much of the phosphorylation on these two proteins is not essential but enhances several steps of mitosis. Of the 65 sites examined on both proteins, phosphorylation of the Mps1 sites Spc29-T18 and Spc29-T240 was shown to be critical for function. Interestingly, these two sites primarily influence distinct successive steps; Spc29-T240 is important for the interaction of Spc29 with Spc42, likely during satellite formation, and Spc29-T18 facilitates insertion of the new SPB into the nuclear envelope and promotes anaphase spindle elongation. Phosphorylation sites within Cdk1 motifs affect function to varying degrees, but mutations only have significant effects in the presence of an MPS1 mutation, supporting a theme of coregulation by these two kinases.

scholarly journals Studies concerning the temporal and genetic control of cell polarity in Saccharomyces cerevisiae.

1991 ◽  
Vol 114 (3) ◽  
pp. 515-532 ◽  
Author(s):  
M Snyder ◽  
S Gehrung ◽  
B D Page
Keyword(s):  
Cell Cycle ◽  
Cell Polarity ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Yeast Cells ◽  
Cell Cycle Distribution ◽  
Restrictive Temperature ◽  
Microtubule Bundle ◽  
Pole Body ◽  
Capture Site

The establishment of cell polarity was examined in the budding yeast, S. cerevisiae. The distribution of a polarized protein, the SPA2 protein, was followed throughout the yeast cell cycle using synchronized cells and cdc mutants. The SPA2 protein localizes to a patch at the presumptive bud site of G1 cells. Later it concentrates at the bud tip in budded cells. At cytokinesis, the SPA2 protein is at the neck between the mother and daughter cells. Analysis of unbudded haploid cells has suggested a series of events that occurs during G1. The SPA2 patch is established very early in G1, while the spindle pole body residues on the distal side of the nucleus. Later, microtubules emanating from the spindle pole body intersect the SPA2 crescent, and the nucleus probably rotates towards the SPA2 patch. By middle G1, most cells contain the SPB on the side of the nucleus proximal to the SPA2 patch, and a long extranuclear microtubule bundle intersects this patch. We suggest that a microtubule capture site exists in the SPA2 staining region that stabilizes the long microtubule bundle; this capture site may be responsible for rotation of the nucleus. Cells containing a polarized distribution of the SPA2 protein also possess a polarized distribution of actin spots in the same region, although the actin staining is much more diffuse. Moreover, cdc4 mutants, which form multiple buds at the restrictive temperature, exhibit simultaneous staining of the SPA2 protein and actin spots in a subset of the bud tips. spa2 mutants contain a polarized distribution of actin spots, and act1-1 and act1-2 mutants often contain a polarized distribution of the SPA2 protein suggesting that the SPA2 protein is not required for localization of the actin spots and the actin spots are not required for localization of the SPA2 protein. cdc24 mutants, which fail to form buds at the restrictive temperature, fail to exhibit polarized localization of the SPA2 protein and actin spots, indicating that the CDC24 protein is directly or indirectly responsible for controlling the polarity of these proteins. Based on the cell cycle distribution of the SPA2 protein, a "cytokinesis tag" model is proposed to explain the mechanism of the non-random positioning of bud sites in haploid yeast cells.

scholarly journals Cdk1 promotes cytokinesis in fission yeast through activation of the septation initiation network

2014 ◽  
Vol 25 (15) ◽  
pp. 2250-2259 ◽  
Author(s):  
Nicole Rachfall ◽  
Alyssa E. Johnson ◽  
Sapna Mehta ◽  
Jun-Song Chen ◽  
Kathleen L. Gould
Keyword(s):  
Cell Cycle ◽  
Spindle Pole Body ◽  
Complete Removal ◽  
Spindle Pole ◽  
Cyclin Dependent Kinase ◽  
Gtpase Activating Protein ◽  
Pole Body ◽  
Kinase Cascade ◽  
Septation Initiation Network ◽  
Cycle Dependent

In Schizosaccharomyces pombe, late mitotic events are coordinated with cytokinesis by the septation initiation network (SIN), an essential spindle pole body (SPB)–associated kinase cascade, which controls the formation, maintenance, and constriction of the cytokinetic ring. It is not fully understood how SIN initiation is temporally regulated, but it depends on the activation of the GTPase Spg1, which is inhibited during interphase by the essential bipartite GTPase-activating protein Byr4-Cdc16. Cells are particularly sensitive to the modulation of Byr4, which undergoes cell cycle–dependent phosphorylation presumed to regulate its function. Polo-like kinase, which promotes SIN activation, is partially responsible for Byr4 phosphorylation. Here we show that Byr4 is also controlled by cyclin-dependent kinase (Cdk1)–mediated phosphorylation. A Cdk1 nonphosphorylatable Byr4 phosphomutant displays severe cell division defects, including the formation of elongated, multinucleate cells, failure to maintain the cytokinetic ring, and compromised SPB association of the SIN kinase Cdc7. Our analyses show that Cdk1-mediated phosphoregulation of Byr4 facilitates complete removal of Byr4 from metaphase SPBs in concert with Plo1, revealing an unexpected role for Cdk1 in promoting cytokinesis through activation of the SIN pathway.

The influence of the microtubule inhibitor, methyl benzimidazol-2-yl-carbamate (MBC) on nuclear division and the cell cycle in Saccharomyces cerevisiae

1980 ◽  
Vol 46 (1) ◽  
pp. 341-352
Author(s):  
R.A. Quinlan ◽  
C.I. Pogson ◽  
K. Gull
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Ultrastructural Examination ◽  
Microtubule Inhibitor ◽  
Microtubule Polymerization ◽  
Pole Body ◽  
Outer Component ◽  
Spindle Microtubules

Methyl benzimidazol-2-yl-carbamate (MBC), at a concentration of 100 microM, has a pronounced effect on the growth of Saccharomyces cerevisiae, resulting in the accumulation of cells as large doublets. We have determined a specific execution point for the effect of MBC on the yeast cell cycle, and have shown that this execution point is between the cycle events of spindle pole body duplication and spindle pole body separation. An ultrastructural examination of the MBC-treated cells revealed the absence of cytoplasmic and spindle microtubules. MBC treatment also produced an altered spindle pole body morphology, causing the disappearance of the outer component. Nuclear size was also markedly increased in the MBC-induced doublet cells, although the septa were completely absent from these doublet cells. It is proposed that MBC inhibits microtubule polymerization, rather than causing the depolymerization of stable microtubules.

scholarly journals Spc98p Directs the Yeast γ-Tubulin Complex into the Nucleus and Is Subject to Cell Cycle-dependent Phosphorylation on the Nuclear Side of the Spindle Pole Body

1998 ◽  
Vol 9 (4) ◽  
pp. 775-793 ◽  
Author(s):  
Gislene Pereira ◽  
Michael Knop ◽  
Elmar Schiebel
Keyword(s):  
Cell Cycle ◽  
Spindle Pole Body ◽  
Mitotic Checkpoint ◽  
Spindle Pole ◽  
Nuclear Localization Sequence ◽  
Checkpoint Control ◽  
Yeast Saccharomyces Cerevisiae ◽  
Pole Body ◽  
Cycle Dependent ◽  
Cytoplasmic Side

In the yeast Saccharomyces cerevisiae, microtubules are organized by the spindle pole body (SPB), which is embedded in the nuclear envelope. Microtubule organization requires the γ-tubulin complex containing the γ-tubulin Tub4p, Spc98p, and Spc97p. The Tub4p complex is associated with cytoplasmic and nuclear substructures of the SPB, which organize the cytoplasmic and nuclear microtubules. Here we present evidence that the Tub4p complex assembles in the cytoplasm and then either binds to the cytoplasmic side of the SPB or is imported into the nucleus followed by binding to the nuclear side of the SPB. Nuclear import of the Tub4p complex is mediated by the essential nuclear localization sequence of Spc98p. Our studies also indicate that Spc98p in the Tub4p complex is phosphorylated at the nuclear, but not at the cytoplasmic, side of the SPB. This phosphorylation is cell cycle dependent and occurs after SPB duplication and nucleation of microtubules by the new SPB and therefore may have a role in mitotic spindle function. In addition, activation of the mitotic checkpoint stimulates Spc98p phosphorylation. The kinase Mps1p, which functions in SPB duplication and mitotic checkpoint control, seems to be involved in Spc98p phosphorylation. Our results also suggest that the nuclear and cytoplasmic Tub4p complexes are regulated differently.

scholarly journals Toxic effects of excess cloned centromeres.

1986 ◽  
Vol 6 (6) ◽  
pp. 2213-2222 ◽  
Author(s):  
B Futcher ◽  
J Carbon
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Copy Number ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Host Cells ◽  
Selectable Markers ◽  
Pole Body ◽  
Copy Numbers ◽  
Yeast Plasmids

Plasmids carrying a Saccharomyces cerevisiae centromere have a copy number of one or two, whereas other yeast plasmids have high copy numbers. The number of CEN plasmids per yeast cell was made artificially high by transforming cells simultaneously with several different CEN plasmids carrying different, independently selectable markers. Some host cells carried five different CEN plasmids and an average total of 13 extra copies of CEN3. Several effects were noted. The copy number of each plasmid was unexpectedly high. The plasmids were mutually unstable. Cultures contained many dead cells. The viable host cells grew more slowly than control cells, even in nonselective medium. There was a pause in the cell cycle at or just before mitosis. We conclude that an excess of centromeres is toxic and that the copy number of centromere plasmids is low partly because of selection against cells carrying multiple centromere plasmids. The toxicity may be caused by competition between the centromeres for some factor present in limiting quantities, e.g., centromere-binding proteins, microtubules, or space on the spindle pole body.

scholarly journals Budding Yeast Bub2 Is Localized at Spindle Pole Bodies and Activates the Mitotic Checkpoint via a Different Pathway from Mad2

1999 ◽  
Vol 145 (5) ◽  
pp. 979-991 ◽  
Author(s):  
Roberta Fraschini ◽  
Elisa Formenti ◽  
Giovanna Lucchini ◽  
Simonetta Piatti
Keyword(s):  
Cell Cycle ◽  
Mitotic Spindle ◽  
Cell Cycle Progression ◽  
Budding Yeast ◽  
Spindle Pole Body ◽  
Mitotic Checkpoint ◽  
Spindle Pole ◽  
Cycle Progression ◽  
Spindle Pole Bodies

The mitotic checkpoint blocks cell cycle progression before anaphase in case of mistakes in the alignment of chromosomes on the mitotic spindle. In budding yeast, the Mad1, 2, 3, and Bub1, 2, 3 proteins mediate this arrest. Vertebrate homologues of Mad1, 2, 3, and Bub1, 3 bind to unattached kinetochores and prevent progression through mitosis by inhibiting Cdc20/APC-mediated proteolysis of anaphase inhibitors, like Pds1 and B-type cyclins. We investigated the role of Bub2 in budding yeast mitotic checkpoint. The following observations indicate that Bub2 and Mad1, 2 probably activate the checkpoint via different pathways: (a) unlike the other Mad and Bub proteins, Bub2 localizes at the spindle pole body (SPB) throughout the cell cycle; (b) the effect of concomitant lack of Mad1 or Mad2 and Bub2 is additive, since nocodazole-treated mad1 bub2 and mad2 bub2 double mutants rereplicate DNA more rapidly and efficiently than either single mutant; (c) cell cycle progression of bub2 cells in the presence of nocodazole requires the Cdc26 APC subunit, which, conversely, is not required for mad2 cells in the same conditions. Altogether, our data suggest that activation of the mitotic checkpoint blocks progression through mitosis by independent and partially redundant mechanisms.

scholarly journals γ-Tubulin plays a key role in inactivating APC/CCdh1 at the G1–S boundary

2012 ◽  
Vol 198 (5) ◽  
pp. 785-791 ◽  
Author(s):  
Heather Edgerton-Morgan ◽  
Berl R. Oakley
Keyword(s):  
Cell Cycle ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Cyclin B ◽  
Anaphase Promoting Complex ◽  
Gene Encoding ◽  
Localization Pattern ◽  
Pole Body ◽  
Dependent Inactivation

A γ-tubulin mutation in Aspergillus nidulans, mipA-D159, causes failure of inactivation of the anaphase-promoting complex/cyclosome (APC/C) in interphase, resulting in failure of cyclin B (CB) accumulation and removal of nuclei from the cell cycle. We have investigated the role of CdhA, the A. nidulans homologue of the APC/C activator protein Cdh1, in γ-tubulin–dependent inactivation of the APC/C. CdhA was not essential, but it targeted CB for destruction in G1, and APC/CCdhA had to be inactivated for the G1–S transition. mipA-D159 altered the localization pattern of CdhA, and deletion of the gene encoding CdhA allowed CB to accumulate in all nuclei in strains carrying mipA-D159. These data indicate that mipA-D159 causes a failure of inactivation of APC/CCdhA at G1–S, perhaps by altering its localization to the spindle pole body, and, thus, that γ-tubulin plays an important role in inactivating APC/CCdhA at this point in the cell cycle.

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