Mitosis and septum formation in the basidiomycete Helicobasidium mompa

1986 ◽  
Vol 64 (1) ◽  
pp. 130-145 ◽  
Author(s):  
Timothy M. Bourett ◽  
David J. McLaughlin
Keyword(s):  
Endoplasmic Reticulum ◽  
Functional Significance ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Multivesicular Bodies ◽  
Spindle Poles ◽  
Astral Microtubule ◽  
Pole Body ◽  
Helicobasidium Mompa ◽  
Spindle Elongation

Mitosis in clampless, dikaryotic hyphae of Helicobasidium mompa (Basidiomycota, Auriculariales sensu lato) was studied in apical and penultimate cells by correlating light microscopic and ultrastructural observations. Mitosis lasts about 10.5 min. In penultimate cells, mitosis occurs in the base of a branch whose initiation involves rupture of the wall. The extranuclear interphase spindle pole body contains two three-layered discs. Prophase is discerned by the polarization of the nucleus into a karyokinetic and a nucleolar region. During prometaphase, the spindle pole body discs move into the plane of the nuclear envelope where they occupy gaps. The spindle pole is enclosed by a cap of endoplasmic reticulum. At metaphase, nuclei lie side by side, the nucleolus resides in a nuclear evagination, and the spindle pole body discs are five layered. At anaphase, both chromatin to pole movement and extensive spindle elongation occur, astral microtubule populations reach a maximum, and multivesicular bodies aggregate at the spindle poles. Septa contain simple pores and form at the site previously occupied by the dividing nuclei. The results are compared with mitotic cycles in higher fungi and their evolutionary, phylogenetic, and functional significance is discussed.

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 A microtubule polymerase cooperates with the kinesin-6 motor and a microtubule cross-linker to promote bipolar spindle assembly in the absence of kinesin-5 and kinesin-14 in fission yeast

2017 ◽  
Vol 28 (25) ◽  
pp. 3647-3659 ◽  
Author(s):  
Masashi Yukawa ◽  
Tomoki Kawakami ◽  
Masaki Okazaki ◽  
Kazunori Kume ◽  
Ngang Heok Tang ◽  
...  
Keyword(s):  
Fission Yeast ◽  
Chromosome Segregation ◽  
Spindle Pole Body ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
Temperature Sensitive ◽  
Bipolar Spindle ◽  
Pole Body ◽  
Cross Linker ◽  
Spindle Elongation

Accurate chromosome segregation relies on the bipolar mitotic spindle. In many eukaryotes, spindle formation is driven by the plus-end–directed motor kinesin-5 that generates outward force to establish spindle bipolarity. Its inhibition leads to the emergence of monopolar spindles with mitotic arrest. Intriguingly, simultaneous inactivation of the minus-end–directed motor kinesin-14 restores spindle bipolarity in many systems. Here we show that in fission yeast, three independent pathways contribute to spindle bipolarity in the absence of kinesin-5/Cut7 and kinesin-14/Pkl1. One is kinesin-6/Klp9 that engages with spindle elongation once short bipolar spindles assemble. Klp9 also ensures the medial positioning of anaphase spindles to prevent unequal chromosome segregation. Another is the Alp7/TACC-Alp14/TOG microtubule polymerase complex. Temperature-sensitive alp7cut7pkl1 mutants are arrested with either monopolar or very short spindles. Forced targeting of Alp14 to the spindle pole body is sufficient to render alp7cut7pkl1 triply deleted cells viable and promote spindle assembly, indicating that Alp14-mediated microtubule polymerization from the nuclear face of the spindle pole body could generate outward force in place of Cut7 during early mitosis. The third pathway involves the Ase1/PRC1 microtubule cross-linker that stabilizes antiparallel microtubules. Our study, therefore, unveils multifaceted interplay among kinesin-dependent and -independent pathways leading to mitotic bipolar spindle assembly.

scholarly journals Proper timing of cytokinesis is regulated by Schizosaccharomyces pombe Etd1

2009 ◽  
Vol 186 (5) ◽  
pp. 739-753 ◽  
Author(s):  
Juan Carlos García-Cortés ◽  
Dannel McCollum
Keyword(s):  
Fission Yeast ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Yeast Protein ◽  
Late Anaphase ◽  
Pole Body ◽  
Spindle Elongation ◽  
Cell Asymmetry ◽  
Guanosine Triphosphatase ◽  
Asymmetric Activation

Cytokinesis must be initiated only after chromosomes have been segregated in anaphase and must be terminated once cleavage is completed. We show that the fission yeast protein Etd1 plays a central role in both of these processes. Etd1 activates the guanosine triphosphatase (GTPase) Spg1 to trigger signaling through the septum initiation network (SIN) pathway and onset of cytokinesis. Spg1 is activated in late anaphase when spindle elongation brings spindle pole body (SPB)–localized Spg1 into proximity with its activator Etd1 at cell tips, ensuring that cytokinesis is only initiated when the spindle is fully elongated. Spg1 is active at just one of the two SPBs during cytokinesis. When the actomyosin ring finishes constriction, the SIN triggers disappearance of Etd1 from the half of the cell with active Spg1, which then triggers Spg1 inactivation. Asymmetric activation of Spg1 is crucial for timely inactivation of the SIN. Together, these results suggest a mechanism whereby cell asymmetry is used to monitor cytoplasmic partitioning to turn off cytokinesis signaling.

scholarly journals Conservative Duplication of Spindle Poles during Meiosis in Saccharomyces cerevisiae

2001 ◽  
Vol 183 (7) ◽  
pp. 2372-2375 ◽  
Author(s):  
Andreas Wesp ◽  
Susanne Prinz ◽  
Gerald R. Fink
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Spore Formation ◽  
Wild Type ◽  
Body Distribution ◽  
Spindle Poles ◽  
Pole Body ◽  
Spindle Pole Bodies ◽  
Type Strains

ABSTRACT During sporulation in diploid Saccharomyces cerevisiae, spindle pole bodies acquire the so-called meiotic plaque, a prerequisite for spore formation. Mpc70p is a component of the meiotic plaque and is thus essential for spore formation. We show here that MPC70/mpc70 heterozygous strains most often produce two spores instead of four and that these spores are always nonsisters. In wild-type strains, Mpc70p localizes to all four spindle pole bodies, whereas in MPC70/mpc70 strains Mpc70p localizes to only two of the four spindle pole bodies, and these are always nonsisters. Our data can be explained by conservative spindle pole body distribution in which the two newly synthesized meiosis II spindle pole bodies of MPC70/mpc70 strains lack Mpc70p.

Assembly and dynamics of an anastral:astral spindle: the meiosis II spindle of Drosophila oocytes

1998 ◽  
Vol 111 (17) ◽  
pp. 2487-2495 ◽  
Author(s):  
S.A. Endow ◽  
D.J. Komma
Keyword(s):  
De Novo ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
The Body ◽  
Central Spindle ◽  
Spindle Poles ◽  
Pole Body ◽  
Microtubule Motor ◽  
Gamma Tubulin ◽  
Meiosis I

The meiosis II spindle of Drosophila oocytes is distinctive in structure, consisting of two tandem spindles with anastral distal poles and an aster-associated spindle pole body between the central poles. Assembly of the anastral:astral meiosis II spindle occurs by reorganization of the meiosis I spindle, without breakdown of the meiosis I spindle. The unusual disk- or ring-shaped central spindle pole body forms de novo in the center of the elongated meiosis I spindle, followed by formation of the central spindle poles. gamma-Tubulin transiently localizes to the central spindle pole body, implying that the body acts as a microtubule nucleating center for assembly of the central poles. Localization of gamma-tubulin to the meiosis II spindle is dependent on the microtubule motor protein, Nonclaret disjunctional (Ncd). Absence of Ncd results in loss of gamma-tubulin localization to the spindle and destabilization of microtubules in the central region of the spindle. Assembly of the anastral:astral meiosis II spindle probably involves rapid reassortment of microtubule plus and minus ends in the center of the meiosis I spindle - this can be accounted for by a model that also accounts for the loss of gamma-tubulin localization to the spindle and destabilization of microtubules in the absence of Ncd.

scholarly journals Direct experimental evidence for the existence, structural basis and function of astral forces during anaphase B in vivo

1991 ◽  
Vol 100 (2) ◽  
pp. 279-288 ◽  
Author(s):  
J.R. Aist ◽  
C.J. Bayles ◽  
W. Tao ◽  
M.W. Berns
Keyword(s):  
Critical Mass ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Structural Basis ◽  
Mitotic Apparatus ◽  
Pole Body ◽  
Spindle Microtubules ◽  
Spindle Elongation ◽  
And Function ◽  
Anaphase B

The existence, structural basis and function of astral forces that are active during anaphase B in the fungus, Nectria haematococca, were revealed by experiments performed on living cells. When one of the two asters of a mitotic apparatus was damaged, the entire mitotic apparatus migrated rapidly in the direction of the opposing astral forces, showing that the force that accelerated spindle pole body separation in earlier experiments is located in the asters. When a strong solution of the antimicrotubule drug, MBC, was applied at anaphase A, tubulin immunocytochemistry showed that both astral and spindle microtubules were destroyed completely in less than a minute. As a result, separation of the spindle pole bodies during anaphase B almost stopped. By contrast, disrupting only the spindle microtubules with a laser microbeam increased the rate of spindle pole body separation more than fourfold. Taken together, these two experiments show that the astral forces are microtubule-dependent. When only one of the two or three bundles of spindle microtubules was broken at very early anaphase B, most such diminished spindles elongated at a normal rate, whereas others elongated at an increased rate. This result suggests that only a critical mass or number of spindle microtubules needs be present for the rate of spindle elongation to be fully governed, and that astral forces can accelerate the elongation of a weakened or diminished spindle.

scholarly journals ADY1, A Novel Gene Required for Prospore Membrane Formation at Selected Spindle Poles inSaccharomyces cerevisiae

2001 ◽  
Vol 12 (9) ◽  
pp. 2646-2659 ◽  
Author(s):  
Changchun Deng ◽  
William S. Saunders
Keyword(s):  
Meiotic Chromosome ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Membrane Formation ◽  
Spindle Poles ◽  
Pole Body ◽  
Spindle Pole Bodies ◽  
Prospore Membrane ◽  
A Cell ◽  
Body Component

ADY1 is identified in a genetic screen for genes on chromosome VIII of Saccharomyces cerevisiae that are required for sporulation. ADY1 is not required for meiotic recombination or meiotic chromosome segregation, but it is required for the formation of four spores inside an ascus. In the absence of ADY1, prospore formation is restricted to mainly one or two spindle poles per cell. Moreover, the two spores in the dyads of the ady1 mutant are predominantly nonsisters, suggesting that the proficiency to form prospores is not randomly distributed to the four spindle poles in theady1 mutant. Interestingly, the meiosis-specific spindle pole body component Mpc54p, which is known to be required for prospore membrane formation, is localized predominantly to only one or two spindle poles per cell in the ady1 mutant. A partially functional Myc-Pfs1p is localized to the nucleus of mononucleate meiotic cells but not to the spindle pole body or prospore membrane. These results suggest that Pfs1p is specifically required for prospore formation at selected spindle poles, most likely by ensuring the functionality of all four spindle pole bodies of a cell during meiosis II.

scholarly journals The Yeast Spindle Pole Body Component Spc72p Interacts with Stu2p and Is Required for Proper Microtubule Assembly

1998 ◽  
Vol 141 (5) ◽  
pp. 1169-1179 ◽  
Author(s):  
Xiaoyue Peter Chen ◽  
Hongwei Yin ◽  
Tim C. Huffaker
Keyword(s):  
Chromosome Segregation ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Microtubule Assembly ◽  
Temperature Sensitive ◽  
Pole Body ◽  
Cytoplasmic Microtubules ◽  
Spindle Elongation

We have previously shown that Stu2p is a microtubule-binding protein and a component of the Saccharomyces cerevisiae spindle pole body (SPB). Here we report the identification of Spc72p, a protein that interacts with Stu2p. Stu2p and Spc72p associate in the two-hybrid system and can be coimmunoprecipitated from yeast extracts. Stu2p and Spc72p also interact with themselves, suggesting the possibility of a multimeric Stu2p-Spc72p complex. Spc72p is an essential component of the SPB and is able to associate with a preexisting SPB, indicating that there is a dynamic exchange between soluble and SPB forms of Spc72p. Unlike Stu2p, Spc72p does not bind microtubules in vitro, and was not observed to localize along microtubules in vivo. A temperature-sensitive spc72 mutation causes defects in SPB morphology. In addition, most spc72 mutant cells lack cytoplasmic microtubules; the few cytoplasmic microtubules that are observed are excessively long, and some of these are unattached to the SPB. spc72 cells are able to duplicate and separate their SPBs to form a bipolar spindle, but spindle elongation and chromosome segregation rarely occur. The chromosome segregation block does not arrest the cell cycle; instead, spc72 cells undergo cytokinesis, producing aploid cells and polyploid cells that contain multiple SPBs.

scholarly journals Dynamic Positioning of Mitotic Spindles in Yeast:

2000 ◽  
Vol 11 (11) ◽  
pp. 3949-3961 ◽  
Author(s):  
Elaine Yeh ◽  
Charlie Yang ◽  
Elaine Chin ◽  
Paul Maddox ◽  
E. D. Salmon ◽  
...  
Keyword(s):  
Spindle Pole Body ◽  
Cytoplasmic Dynein ◽  
Spindle Pole ◽  
Nuclear Movement ◽  
Yeast Saccharomyces Cerevisiae ◽  
Anaphase Onset ◽  
Astral Microtubule ◽  
Bud Neck ◽  
Microtubule Growth ◽  
Spindle Elongation

In the budding yeast Saccharomyces cerevisiae, movement of the mitotic spindle to a predetermined cleavage plane at the bud neck is essential for partitioning chromosomes into the mother and daughter cells. Astral microtubule dynamics are critical to the mechanism that ensures nuclear migration to the bud neck. The nucleus moves in the opposite direction of astral microtubule growth in the mother cell, apparently being “pushed” by microtubule contacts at the cortex. In contrast, microtubules growing toward the neck and within the bud promote nuclear movement in the same direction of microtubule growth, thus “pulling” the nucleus toward the bud neck. Failure of “pulling” is evident in cells lacking Bud6p, Bni1p, Kar9p, or the kinesin homolog, Kip3p. As a consequence, there is a loss of asymmetry in spindle pole body segregation into the bud. The cytoplasmic motor protein, dynein, is not required for nuclear movement to the neck; rather, it has been postulated to contribute to spindle elongation through the neck. In the absence of KAR9,dynein-dependent spindle oscillations are evident before anaphase onset, as are postanaphase dynein-dependent pulling forces that exceed the velocity of wild-type spindle elongation threefold. In addition, dynein-mediated forces on astral microtubules are sufficient to segregate a 2N chromosome set through the neck in the absence of spindle elongation, but cytoplasmic kinesins are not. These observations support a model in which spindle polarity determinants (BUD6, BNI1, KAR9) and cytoplasmic kinesin (KIP3) provide directional cues for spindle orientation to the bud while restraining the spindle to the neck. Cytoplasmic dynein is attenuated by these spindle polarity determinants and kinesin until anaphase onset, when dynein directs spindle elongation to distal points in the mother and bud.

Sign in / Sign up

Export Citation Format

Share Document