scholarly journals KAR5 Encodes a Novel Pheromone-inducible Protein Required for Homotypic Nuclear Fusion

1997 ◽  
Vol 139 (5) ◽  
pp. 1063-1076 ◽  
Author(s):  
Christopher T. Beh ◽  
Valeria Brizzio ◽  
Mark D. Rose
Keyword(s):  
Membrane Fusion ◽  
Nuclear Membrane ◽  
Nuclear Fusion ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Deletion Mutations ◽  
Pheromone Response Pathway ◽  
Pole Body ◽  
Inducible Protein ◽  
Novel Protein

KAR5 is required for membrane fusion during karyogamy, the process of nuclear fusion during yeast mating. To investigate the molecular mechanism of nuclear fusion, we cloned and characterized the KAR5 gene and its product. KAR5 is a nonessential gene, and deletion mutations produce a bilateral defect in the homotypic fusion of yeast nuclei. KAR5 encodes a novel protein that shares similarity with a protein in Schizosaccharomyces pombe that may play a similar role in nuclear fusion. Kar5p is induced as part of the pheromone response pathway, suggesting that this protein uniquely plays a specific role during mating in nuclear membrane fusion. Kar5p is a membrane protein with its soluble domain entirely contained within the lumen of the endoplasmic reticulum. In pheromone-treated cells, Kar5p was localized to the vicinity of the spindle pole body, the initial site of fusion between haploid nuclei during karyogamy. We propose that Kar5p is required for the completion of nuclear membrane fusion and may play a role in the organization of the membrane fusion complex.

scholarly journals Spindle pole body-anchored Kar3 drives the nucleus along microtubules from another nucleus in preparation for nuclear fusion during yeast karyogamy

2013 ◽  
Vol 27 (3) ◽  
pp. 335-349 ◽  
Author(s):  
R. Gibeaux ◽  
A. Z. Politi ◽  
F. Nedelec ◽  
C. Antony ◽  
M. Knop
Keyword(s):  
Nuclear Fusion ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Pole Body

scholarly journals Requirement of the spindle pole body for targeting and/or tethering proteins to the inner nuclear membrane

Nucleus ◽  
2014 ◽  
Vol 5 (4) ◽  
pp. 352-366 ◽  
Author(s):  
Greetchen Diaz-Muñoz ◽  
Terri A Harchar ◽  
Tsung-Po Lai ◽  
Kuo-Fang Shen ◽  
Anita K Hopper
Keyword(s):  
Nuclear Membrane ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Inner Nuclear Membrane ◽  
Pole Body

scholarly journals Targeting of Nbp1 to the inner nuclear membrane is essential for spindle pole body duplication

2011 ◽  
Vol 30 (16) ◽  
pp. 3337-3352 ◽  
Author(s):  
Thomas Kupke ◽  
Leontina Di Cecco ◽  
Hans-Michael Müller ◽  
Annett Neuner ◽  
Frank Adolf ◽  
...  
Keyword(s):  
Nuclear Membrane ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Inner Nuclear Membrane ◽  
Pole Body

Ultrastructure of mitosis and the spindle pole body cycle in the smut fungus, Tilletia foetida

1985 ◽  
Vol 63 (1) ◽  
pp. 86-96 ◽  
Author(s):  
James A. Hoffmann ◽  
Blair J. Goates
Keyword(s):  
Nuclear Membrane ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Dense Layer ◽  
Double Structure ◽  
Pole Body ◽  
Cytoplasmic Microtubules ◽  
Spindle Microtubules ◽  
Dense Chromatin ◽  
Tilletia Foetida

The interphase nucleus in secondary sporidia of Tilletia foetida consists of mostly diffuse chromatin, one or two nucleoli, and an area of heterochromatin located opposite an electron-dense, extranuclear spindle pole body (SPB). The interphase SPB is an oval- to bar-shaped, double-structured disc that has a crystallinelike substructure. During nuclear migration into nascent sporidia, SPBs and nucleoli are randomly oriented. At the onset of division, chromatin begins to condense and the SPB becomes located on a nuclear protuberance. Cytoplasmic microtubules terminate at the SPBs and multivesicular bodies surround the SPBs from the early stages of SPB division to early postdivision. SPB discs become spheroid and each develops a medial, dense layer. Then, a basal, dense layer develops and elongates as the SPBs separate and become positioned on opposite sides of the nuclear protuberance. The nuclear membrane opens opposite the SPB during SPB division. The nucleolus is extruded into a nuclear bleb and degenerates. SPBs migrate to opposing sides of the nucleus and become diffuse as a microtubular spindle develops between them. Some spindle microtubules terminate at dense chromatin patches that are contiguous with the major mass of chromatin surrounding the spindle. During late division stages, spindle microtubules often appear to be closely juxtaposed. Except for polar openings adjacent to the SPBs, the nuclear membrane is entire until late division when it degenerates in the midregion of the nucleus. During early postdivision, the SPB condenses into a small, dense sphere as the chromatin and heterochromatin opposite the SPB become diffuse. The SPB then elongates into a dense bar and SPB material increases, except at the midportion, reforming the double structure of interphase.

Somatic nuclear division in the sporidia of Ustilago violacea. IV. Microtubules and the spindle-pole body

1976 ◽  
Vol 22 (4) ◽  
pp. 507-522 ◽  
Author(s):  
N. H. Poon ◽  
A. W. Day
Keyword(s):  
Nuclear Membrane ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Control Center ◽  
Ustilago Violacea ◽  
Membrane Breakdown ◽  
Pole Body ◽  
Free Region ◽  
Nuclear Rotation ◽  
Anther Smut

In unbudded cells of the anther smut fungus Ustilago violacea there is a dome-shaped spindle-pole body (SPB) consisting of a core 0.1 μm in diameter surrounded by a ribosome-free region 0.3–0.4 μm in diameter lying in a pocket of the nuclear membrane. After budding the nucleus moves towards the bud and begins to rotate rapidly. At about this stage the SPB divides into two parallel bars each about 0.1–0.15 μm in diameter and 0.3 μm long, separated by a distance of about 0.3 μm. Microtubules associated with the nuclear membrane but not with the SPB are present at the time of nuclear rotation. These microtubules disappear when rotation stops. Microtubules attached to the SPB are found during migration of the chromatinic portion of the nucleus into the bud cell. These microtubules disappear when migration stops and the nuclear membrane begins to break down. The twin SPB bars appear to move into the nucleus through a break in the membrane and begin to move apart forming a spindle about 1 μm long. Chromosomal microtubules (one per kinetochore) were found in several serial sections, and in addition there appeared to be several continuous microtubules present. The separation of the two chromatinic masses appeared to result from elongation of the continuous microtubules to about 3 μm long. Cytoplasmic microtubules and spindle microtubules were both found attached to the SPB as it elongated and one nucleus returned to the mother cell.The paper concludes with a discussion of the SPB as a multifunctional control center affecting nuclear migration, spindle formation, membrane breakdown and synthesis, karyogamy, conjugation, budding, chromosomal movement, replication, and disjunction.

scholarly journals BIK1, a protein required for microtubule function during mating and mitosis in Saccharomyces cerevisiae, colocalizes with tubulin.

1990 ◽  
Vol 111 (6) ◽  
pp. 2573-2586 ◽  
Author(s):  
V Berlin ◽  
C A Styles ◽  
G R Fink
Keyword(s):  
Synthetic Lethality ◽  
Nuclear Fusion ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Microtubule Assembly ◽  
Chromosome Loss ◽  
Physical Interaction ◽  
Pole Body ◽  
Cytoplasmic Microtubules ◽  
And Function

BIK1 function is required for nuclear fusion, chromosome disjunction, and nuclear segregation during mitosis. The BIK1 protein colocalizes with tubulin to the spindle pole body and mitotic spindle. Synthetic lethality observed in double mutant strains containing a mutation in the BIK1 gene and in the gene for alpha- or beta-tubulin is consistent with a physical interaction between BIK1 and tubulin. Furthermore, over- or underexpression of BIK1 causes aberrant microtubule assembly and function, bik1 null mutants are viable but contain very short or undetectable cytoplasmic microtubules. Spindle formation often occurs strictly within the mother cell, probably accounting for the many multinucleate and anucleate bik1 cells. Elevated levels of chromosome loss in bik1 cells are indicative of defective spindle function. Nuclear fusion is blocked in bik1 x bik1 zygotes, which have truncated cytoplasmic microtubules. Cells overexpressing BIK1 initially have abnormally short or nonexistent spindle microtubules and long cytoplasmic microtubules. Subsequently, cells lose all microtubule structures, coincident with the arrest of division. Based on these results, we propose that BIK1 is required stoichiometrically for the formation or stabilization of microtubules during mitosis and for spindle pole body fusion during conjugation.

Spindle pole body fusion in the smut fungus Tilletia foetida

1986 ◽  
Vol 64 (6) ◽  
pp. 1221-1223 ◽  
Author(s):  
Blair J. Goates ◽  
James A. Hoffmann
Keyword(s):  
Nuclear Fusion ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Smut Fungus ◽  
Narrow Region ◽  
Pole Body ◽  
Spindle Pole Bodies ◽  
Tilletia Foetida

Fusion of double-structured, interphase spindle pole bodies (SPBs) occurred before nuclear fusion in heterokaryotic secondary sporidia. The SPBs of two separate nuclei were juxtaposed with their long axes perpendicular to each other. Also, SPBs were observed oriented with their long axes parallel and fused to each other at both ends. Fusion apparently continued toward the midportion of the SPBs. Nuclei were observed joined together in a narrow region. These nuclei appeared to share a single SPB that was located opposite to a protuberance on both nuclei. Following fusion, the SPB apparently returned to an interphase structure.

scholarly journals The SUN Protein Mps3 Is Required for Spindle Pole Body Insertion into the Nuclear Membrane and Nuclear Envelope Homeostasis

PLoS Genetics ◽  
2011 ◽  
Vol 7 (11) ◽  
pp. e1002365 ◽  
Author(s):  
Jennifer M. Friederichs ◽  
Suman Ghosh ◽  
Christine J. Smoyer ◽  
Scott McCroskey ◽  
Brandon D. Miller ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
The Sun ◽  
Pole Body

scholarly journals Membrane proteins Bqt3 and -4 anchor telomeres to the nuclear envelope to ensure chromosomal bouquet formation

2009 ◽  
Vol 187 (3) ◽  
pp. 413-427 ◽  
Author(s):  
Yuji Chikashige ◽  
Miho Yamane ◽  
Kasumi Okamasa ◽  
Chihiro Tsutsumi ◽  
Tomoko Kojidani ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Fission Yeast ◽  
Nuclear Membrane ◽  
Meiotic Prophase ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Null Mutant ◽  
Vegetative Cells ◽  
Nuclear Membranes ◽  
Pole Body

In many organisms, telomeres cluster to form a bouquet arrangement of chromosomes during meiotic prophase. Previously, we reported that two meiotic proteins, Bqt1 and -2, are required for tethering telomeres to the spindle pole body (SPB) during meiotic prophase in fission yeast. This study has further identified two novel, ubiquitously expressed inner nuclear membrane (INM) proteins, Bqt3 and -4, which are required for bouquet formation. We found that in the absence of Bqt4, telomeres failed to associate with the nuclear membranes in vegetative cells and consequently failed to cluster to the SPB in meiotic prophase. In the absence of Bqt3, Bqt4 protein was degraded during meiosis, leading to a phenotype similar to that of the bqt4-null mutant. Collectively, these results show that Bqt4 anchors telomeres to the INM and that Bqt3 protects Bqt4 from protein degradation. Interestingly, the functional integrity of telomeres is maintained even when they are separated from the nuclear envelope in vegetative cells.

The transition of cells of the fission yeast beta-tubulin mutant nda3-311 as seen by freeze-substitution electron microscopy. Requirement of functional tubulin for spindle pole body duplication

1990 ◽  
Vol 96 (2) ◽  
pp. 275-282
Author(s):  
T. Kanbe ◽  
Y. Hiraoka ◽  
K. Tanaka ◽  
M. Yanagida
Keyword(s):  
Electron Microscopy ◽  
Cross Section ◽  
Nuclear Membrane ◽  
Mitotic Spindle ◽  
Spindle Pole Body ◽  
Freeze Substitution ◽  
Spindle Pole ◽  
Permissive Temperature ◽  
Beta Tubulin ◽  
Pole Body

A previous fluorescence light-microscopic study showed that the fission yeast cold-sensitive beta-tubulin mutant nda3-311 was arrested with rod-like condensed chromosomes in a mitotic state at the restrictive temperature. Upon transfer to the permissive temperature, a spindle was formed and the nucleus was divided. In the present study, we employed freeze-substitution electron microscopy to examine the ultrastructure of arrested and released nda3-311 cells. In arrested cells, a single, displaced nucleus was seen with a single spindle pole body. Therefore, spindle pole body duplication seemed to require functional beta-tubulin. The nuclear membrane was highly deformed with a leaf-like profile in cross-section, possibly due to an interaction with the rod-like, condensed chromosomes. Upon transfer to the permissive temperature, the spindle pole duplicated and the daughter spindle pole bodies rapidly migrated to the opposite ends of the nucleus, accompanied by the formation of the mitotic spindle. Elongation of the nuclear envelope occurred with concomitant spindle extension, as in a wild-type mitosis. The deformed nuclear membrane became smooth and described a convex curve. The numerous vacuoles that are seen in the arrested cells decreased in number and increased in size. Septation was completed, leaving the two divided nuclei in one half of the cell. Hexagonally arranged microtubules, apparently forming the mitotic spindle, were observed in a cross-section of a cell after return to the permissive conditions.

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