Faculty Opinions recommendation of Gamma-tubulin complex-mediated anchoring of spindle microtubules to spindle-pole bodies requires Msd1 in fission yeast.

The minus ends of spindle microtubules are anchored to a microtubule-organizing center. The conserved Msd1/SSX2IP proteins are localized to the spindle pole body (SPB) and the centrosome in fission yeast and humans, respectively, and play a critical role in microtubule anchoring. In this paper, we show that fission yeast Msd1 forms a ternary complex with another conserved protein, Wdr8, and the minus end–directed Pkl1/kinesin-14. Individual deletion mutants displayed the identical spindle-protrusion phenotypes. Msd1 and Wdr8 were delivered by Pkl1 to mitotic SPBs, where Pkl1 was tethered through Msd1–Wdr8. The spindle-anchoring defect imposed by msd1/wdr8/pkl1 deletions was suppressed by a mutation of the plus end–directed Cut7/kinesin-5, which was shown to be mutual. Intriguingly, Pkl1 motor activity was not required for its anchoring role once targeted to the SPB. Therefore, spindle anchoring through Msd1–Wdr8–Pkl1 is crucial for balancing the Cut7/kinesin-5–mediated outward force at the SPB. Our analysis provides mechanistic insight into the spatiotemporal regulation of two opposing kinesins to ensure mitotic spindle bipolarity.

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Paired arrangement of kinetochores together with microtubule pivoting and dynamics drive kinetochore capture in meiosis I

Scientific Reports ◽

10.1038/srep25736 ◽

2016 ◽

Vol 6 (1) ◽

Cited By ~ 10

Author(s):

Gheorghe Cojoc ◽

Ana-Maria Florescu ◽

Alexander Krull ◽

Anna H. Klemm ◽

Nenad Pavin ◽

...

Keyword(s):

Cell Division ◽

Fission Yeast ◽

General Feature ◽

Protein Complexes ◽

Spindle Pole ◽

Single Object ◽

Homologous Chromosomes ◽

Angular Movement ◽

Spindle Microtubules ◽

Meiosis I

Abstract Kinetochores are protein complexes on the chromosomes, whose function as linkers between spindle microtubules and chromosomes is crucial for proper cell division. The mechanisms that facilitate kinetochore capture by microtubules are still unclear. In the present study, we combine experiments and theory to explore the mechanisms of kinetochore capture at the onset of meiosis I in fission yeast. We show that kinetochores on homologous chromosomes move together, microtubules are dynamic and pivot around the spindle pole, and the average capture time is 3–4 minutes. Our theory describes paired kinetochores on homologous chromosomes as a single object, as well as angular movement of microtubules and their dynamics. For the experimentally measured parameters, the model reproduces the measured capture kinetics and shows that the paired configuration of kinetochores accelerates capture, whereas microtubule pivoting and dynamics have a smaller contribution. Kinetochore pairing may be a general feature that increases capture efficiency in meiotic cells.

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The Spindle Pole Bodies Facilitate Nuclear Envelope Division during Closed Mitosis in Fission Yeast

PLoS Biology ◽

10.1371/journal.pbio.0050170 ◽

2007 ◽

Vol 5 (7) ◽

pp. e170 ◽

Cited By ~ 21

Author(s):

Liling Zheng ◽

Cindi Schwartz ◽

Valentin Magidson ◽

Alexey Khodjakov ◽

Snezhana Oliferenko

Keyword(s):

Nuclear Envelope ◽

Fission Yeast ◽

Spindle Pole ◽

Spindle Pole Bodies

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Asymmetry of the spindle pole bodies and spg1p GAP segregation during mitosis in fission yeast

Journal of Cell Science ◽

10.1242/jcs.112.14.2313 ◽

1999 ◽

Vol 112 (14) ◽

pp. 2313-2321 ◽

Cited By ~ 22

Author(s):

L. Cerutti ◽

V. Simanis

Keyword(s):

Cell Cycle ◽

Fission Yeast ◽

Spindle Pole Body ◽

Mitotic Cell ◽

Spindle Pole ◽

The Other ◽

Septum Formation ◽

Spindle Pole Bodies ◽

Interphase Cells ◽

Early Mitosis

In the fission yeast Schizosaccharomyces pombe, the onset of septum formation is induced by a signal transduction network involving several protein kinases and a GTPase switch. One of the roles of the spg1p GTPase is to localise the cdc7p protein kinase to the poles of the mitotic spindle, from where the onset of septation is thought to be signalled at the end of mitosis. Immunofluorescence studies have shown that cdc7p is located on both spindle pole bodies early in mitosis, but only on one during the later stages of anaphase. This is mediated by inactivation of spg1p on one pole before the other. The GAP for spg1p is a complex of two proteins, cdc16p and byr4p. Localisation of cdc16p and byr4p by indirect immunofluorescence during the mitotic cell cycle showed that both proteins are present on the spindle pole body in interphase cells. During mitosis, byr4p is seen first on both poles of the spindle, then on only one. This occurs prior to cdc7p becoming asymmetric. In contrast, the signal due to cdc16p decreases to a low level during early mitosis, before being seen strongly on the same pole as byr4p. Double staining indicates that this is the opposite pole to that which retains cdc7p in late anaphase. Examination of the effect of inactivating cdc16p at various stages of the cell cycle suggests that cdc16p, together with cdc2p plays a role in restraining septum formation during interphase. The asymmetric inactivation of spg1p is mediated by recruitment of the cdc16p-byr4p GAP to one of the poles of the spindle before the other, and the asymmetry of the spindle pole bodies may be established early during mitosis. Moreover, the spindle pole bodies appear to be non-equivalent even after division has been completed.

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The role of gamma-tubulin in mitotic spindle formation and cell cycle progression in Aspergillus nidulans

Journal of Cell Science ◽

10.1242/jcs.110.5.623 ◽

1997 ◽

Vol 110 (5) ◽

pp. 623-633 ◽

Cited By ~ 3

Author(s):

M.A. Martin ◽

S.A. Osmani ◽

B.R. Oakley

Keyword(s):

Cell Cycle ◽

Mitotic Spindle ◽

Cell Cycle Progression ◽

Spindle Pole ◽

Microtubule Assembly ◽

Cytoplasmic Microtubule ◽

Cycle Progression ◽

Spindle Microtubules ◽

Gamma Tubulin

gamma-Tubulin has been hypothesized to be essential for the nucleation of the assembly of mitotic spindle microtubules, but some recent results suggest that this may not be the case. To clarify the role of gamma-tubulin in microtubule assembly and cell-cycle progression, we have developed a novel variation of the gene disruption/heterokaryon rescue technique of Aspergillus nidulans. We have used temperature-sensitive cell-cycle mutations to synchronize germlings carrying a gamma-tubulin disruption and observe the phenotypes caused by the disruption in the first cell cycle after germination. Our results indicate that gamma-tubulin is absolutely required for the assembly of mitotic spindle microtubules, a finding that supports the hypothesis that gamma-tubulin is involved in spindle microtubule nucleation. In the absence of functional gamma-tubulin, nuclei are blocked with condensed chromosomes for about the length of one cell cycle before chromatin decondenses without nuclear division. Our results indicate that gamma-tubulin is not essential for progression from G1 to G2, for entry into mitosis nor for spindle pole body replication. It is also not required for reactivity of spindle pole bodies with the MPM-2 antibody which recognizes a phosphoepitope important to mitotic spindle formation. Finally, it does not appear to be absolutely required for cytoplasmic microtubule assembly but may play a role in the formation of normal cytoplasmic microtubule arrays.

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Synergistic role of fission yeast Alp16GCP6 and Mzt1MOZART1 in γ-tubulin complex recruitment to mitotic spindle pole bodies and spindle assembly

Molecular Biology of the Cell ◽

10.1091/mbc.e15-08-0577 ◽

2016 ◽

Vol 27 (11) ◽

pp. 1753-1763 ◽

Cited By ~ 19

Author(s):

Hirohisa Masuda ◽

Takashi Toda

Keyword(s):

Fission Yeast ◽

Mitotic Spindle ◽

Spindle Assembly Checkpoint ◽

Synthetic Lethality ◽

Spindle Assembly ◽

Spindle Pole ◽

Microtubule Assembly ◽

Spindle Microtubule ◽

Spindle Pole Bodies ◽

Mitotic Spindle Pole

In fission yeast, γ-tubulin ring complex (γTuRC)–specific components Gfh1GCP4, Mod21GCP5, and Alp16GCP6 are nonessential for cell growth. Of these deletion mutants, only alp16Δ shows synthetic lethality with temperature-sensitive mutants of Mzt1MOZART1, a component of the γTuRC required for recruitment of the complex to microtubule-organizing centers. γ-Tubulin small complex levels at mitotic spindle pole bodies (SPBs, the centrosome equivalent in fungi) and microtubule levels for preanaphase spindles are significantly reduced in alp16Δ cells but not in gfh1Δ or mod21Δ cells. Furthermore, alp16Δ cells often form monopolar spindles and frequently lose a minichromosome when the spindle assembly checkpoint is inactivated. Alp16GCP6 promotes Mzt1-dependent γTuRC recruitment to mitotic SPBs and enhances spindle microtubule assembly in a manner dependent on its expression levels. Gfh1GCP4 and Mod21GCP5 are not required for Alp16GCP6-dependent γTuRC recruitment. Mzt1 has an additional role in the activation of the γTuRC for spindle microtubule assembly. The ratio of Mzt1 to γTuRC levels for preanaphase spindles is higher than at other stages of the cell cycle. Mzt1 overproduction enhances spindle microtubule assembly without affecting γTuRC levels at mitotic SPBs. We propose that Alp16GCP6 and Mzt1 act synergistically for efficient bipolar spindle assembly to ensure faithful chromosome segregation.

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Kinetochore capture by spindle microtubules: why fission yeast may prefer pivoting to search-and-capture

10.1101/673723 ◽

2019 ◽

Cited By ~ 1

Author(s):

Indrani Nayak ◽

Dibyendu Das ◽

Amitabha Nandi

Keyword(s):

Fission Yeast ◽

Cell Biology ◽

Rotational Diffusion ◽

Spindle Pole Body ◽

Experimental Studies ◽

Spindle Pole ◽

Capture Process ◽

Geometrical Constraints ◽

The Common ◽

Spindle Microtubules

The mechanism by which microtubules find kinetochores during spindle formation is a key question in cell biology. Previous experimental studies have shown that although search-and-capture of kinetochores by dynamic microtubules is a dominant mechanism in many organisms, several other capture mechanisms are also possible. One such mechanism reported in Schizosaccharomyces pombe shows that microtubules can exhibit a prolonged pause between growth and shrinkage. During the pause, the microtubules pivoted at the spindle pole body search for the kinetochores by performing an angular diffusion. Is the latter mechanism purely accidental, or could there be any physical advantage underlying its selection? To compare the efficiency of these two mechanisms, we numerically study distinct models and compute the timescales of kinetochore capture as a function of microtubule number N. We find that the capture timescales have non-trivial dependences on microtubule number, and one mechanism may be preferred over the other depending on this number. While for small N (as in fission yeast), the typical capture times due to rotational diffusion are lesser than those for search-and-capture, the situation is reversed beyond a certain N. The capture times for rotational diffusion tend to saturate due to geometrical constraints, while those for search-and-capture reduce monotonically with increasing N making it physically more efficient. The results provide a rationale for the common occurrence of classic search-and-capture process in many eukaryotes which have few hundreds of dynamic microtubules, as well as justify exceptions in cells with fewer microtubules.

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Mitosis in the fission yeast Schizosaccharomyces pombe as revealed by freeze-substitution electron microscopy

Journal of Cell Science ◽

10.1242/jcs.80.1.253 ◽

1986 ◽

Vol 80 (1) ◽

pp. 253-268

Author(s):

K. Tanaka ◽

T. Kanbe

Keyword(s):

Schizosaccharomyces Pombe ◽

Mitotic Spindle ◽

Nuclear Division ◽

Freeze Substitution ◽

Spindle Pole ◽

Nuclear Space ◽

Spindle Pole Bodies ◽

Transmission Electron ◽

Cytoplasmic Microtubules ◽

Spindle Microtubules

Nuclear division in Schizosaccharomyces pombe has been studied in transmission electron micrographs of sections of cells fixed by a method of freeze-substitution. We have found cytoplasmic microtubules in the vicinity of the spindle pole bodies and two kinds of microtubules, short discontinuous ones and long, parallel ones in the intranuclear mitotic spindle. For most of the time taken by nuclear division the spindle pole bodies face each other squarely across the nuclear space but early in mitosis they briefly appear twisted out of alignment with each other, thereby imparting a sigmoidal shape to the bundle of spindle microtubules extending between them. This configuration is interpreted as indicating active participation of the spindle in the initial elongation of the dividing nucleus. It is proposed that mitosis is accompanied by the shortening of chromosomal microtubules simultaneously with the elongation of the central pole-to-pole bundle of microtubules of the intranuclear spindle. Daughter nuclei are separated by the sliding apart of interdigitating microtubules of the spindle at telophase. Some of the latter bear dense knobs at their ends.

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Gamma-tubulin reorganization during mouse fertilization and early development

Journal of Cell Science ◽

10.1242/jcs.104.2.383 ◽

1993 ◽

Vol 104 (2) ◽

pp. 383-389 ◽

Cited By ~ 11

Author(s):

M.J. Palacios ◽

H.C. Joshi ◽

C. Simerly ◽

G. Schatten

Keyword(s):

Early Development ◽

Basal Body ◽

Spindle Pole ◽

Meiotic Spindle ◽

Cytoplasmic Microtubule ◽

Mouse Oocytes ◽

Spindle Pole Bodies ◽

Preimplantation Stage ◽

Pericentriolar Material ◽

Gamma Tubulin

gamma-Tubulin, a component of spindle pole bodies in fungal cells and pericentriolar material in vertebrate cells, is thought to play a role in the nucleation of microtubule growth and to define their polarity. In contrast to the adult somatic cells, microtubules are nucleated in the absence of centrioles in mammalian oocytes and early embryos. By studying acentriolar mouse oocytes and their early development following fertilization, we show that gamma-tubulin antibody crossreacts with a 50,000 M(r) protein in unfertilized mouse oocytes and demonstrate that gamma-tubulin distribution is rearranged dramatically during fertilization. In unfertilized mouse oocytes, gamma-tubulin is concentrated in the broad spindle poles of meiotic spindle (MII) and as the distinct foci which form the centers of the cytoplasmic microtubule asters (cytasters). The integrity of these gamma-tubulin foci and their cytoplasmic location is maintained during the drug- or cold-induced depolymerization of microtubules. gamma-Tubulin is also found in the basal body of the mouse sperm. During fertilization, the gamma-tubulin is found at the cytastral centers as well as in the incorporated sperm basal body complex, and the gamma-tubulin foci coalesce at the perinuclear microtubule organizing regions of the two pronuclei at the first mitotic prophase. During mitosis, gamma-tubulin is found associated with broad bands that form the poles of the first mitotic spindle. By the late preimplantation stage, when newly generated centrioles have been reported to arise, gamma-tubulin remains localized at the centrosome of mitotic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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