Light and electron microscopy of conjugation in the yeast, Schizosaccharomyces octosporus

1982 ◽  
Vol 28 (9) ◽  
pp. 1059-1077 ◽  
Author(s):  
M.-L. Ashton ◽  
P. B. Moens
Keyword(s):  
Electron Microscopy ◽  
Light And Electron Microscopy ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Microscope Level ◽  
Nuclear Movement ◽  
Light Microscope Level ◽  
Spindle Pole Bodies ◽  
Interference Contrast Microscopy ◽  
Fluorescent Spot

Conjugation in Schizosaccharomyces octosporus is described through the use of interference contrast microscopy, fluorescence microscopy, and electron microscopy of serial sections. At the light microscope level, mating was frequently observed to occur between cells of common ancestry. Fluorescent staining of the nuclei showed that nuclear migration occurs prior to karyogamy, and following diploidization the nucleus then migrates to the end of the cell. A brightly fluorescent spot was found at the apex of the migration nucleus. At the electron microscope level, the results showed that nuclear movement occurs in the presence of cytoplasmic microtubules that are associated with the spindle pole body, the conjugatory nuclei first fuse at or near the spindle pole bodies, and fusion of the spindle bodies occurs apparently by stacking one onto the other.

scholarly journals ULTRASTRUCTURE AND TIME COURSE OF MITOSIS IN THE FUNGUS FUSARIUM OXYSPORUM

1972 ◽  
Vol 55 (2) ◽  
pp. 368-389 ◽  
Author(s):  
James R. Aist ◽  
P. H. Williams
Keyword(s):  
Electron Microscopy ◽  
Fusarium Oxysporum ◽  
Time Course ◽  
Light And Electron Microscopy ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Metaphase Chromosomes ◽  
Mitotic Apparatus ◽  
Spindle Poles ◽  
Spindle Microtubules

Mitosis in Fusarium oxysporum Schlect. was studied by light and electron microscopy. The average times required for the stages of mitosis, as determined from measurements made on living nuclei, were as follows: prophase, 70 sec; metaphase, 120 sec; anaphase, 13 sec; and telophase, 125 sec, for a total of 5.5 min. New postfixation procedures were developed specifically to preserve the fine-structure of the mitotic apparatus. Electron microscopy of mitotic nuclei revealed a fibrillo-granular, extranuclear Spindle Pole Body (SPB) at each pole of the intranuclear, microtubular spindles. Metaphase chromosomes were attached to spindle microtubules via kinetochores, which were found near the spindle poles at telophase. The still-intact, original nuclear envelope constricted around the incipient daughter nuclei during telophase.

scholarly journals Structural role of Sfi1p–centrin filaments in budding yeast spindle pole body duplication

2006 ◽  
Vol 173 (6) ◽  
pp. 867-877 ◽  
Author(s):  
Sam Li ◽  
Alan M. Sandercock ◽  
Paul Conduit ◽  
Carol V. Robinson ◽  
Roger L. Williams ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Saccharomyces Cerevisiae ◽  
Crystal Structures ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Pole Body ◽  
Spindle Pole Bodies ◽  
N Terminus ◽  
Α Helix

Centrins are calmodulin-like proteins present in centrosomes and yeast spindle pole bodies (SPBs) and have essential functions in their duplication. The Saccharomyces cerevisiae centrin, Cdc31p, binds Sfi1p on multiple conserved repeats; both proteins localize to the SPB half-bridge, where the new SPB is assembled. The crystal structures of Sfi1p–centrin complexes containing several repeats show Sfi1p as an α helix with centrins wrapped around each repeat and similar centrin–centrin contacts between each repeat. Electron microscopy (EM) shadowing of an Sfi1p–centrin complex with 15 Sfi1 repeats and 15 centrins bound showed filaments 60 nm long, compatible with all the Sfi1 repeats as a continuous α helix. Immuno-EM localization of the Sfi1p N and C termini showed Sfi1p–centrin filaments spanning the length of the half-bridge with the Sfi1p N terminus at the SPB. This suggests a model for SPB duplication where the half-bridge doubles in length by association of the Sfi1p C termini, thereby providing a new Sfi1p N terminus to initiate SPB assembly.

scholarly journals Meiosis in Coprinus. VIII. A time-course study of the fusion and division of the spindle pole body during meiosis.

1978 ◽  
Vol 76 (3) ◽  
pp. 761-766 ◽  
Author(s):  
B C Lu
Keyword(s):  
Electron Microscopy ◽  
Time Course ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Coprinus Cinereus ◽  
Synaptonemal Complexes ◽  
Pole Body ◽  
Spindle Pole Bodies ◽  
Time Course Study ◽  
Metaphase I

The time-course study of meiosis in the fungus Coprinus cinereus (C. lagopus) by electron microscopy reveals that two monoglobular spindle pole bodies (SPB's) of prekaryogamy nuclei come together during karyogamy and are fused. The fusion SPB of postkaryogamy nucleus persists through zygotene and pachytene as evidenced by the presence of axial components and synaptonemal complexes. At early diplotene, the SPB divides. The divided SPB takes on a diglobular form, which grows in size to form two daughter SPB's. These separate and move to opposite poles at metaphase I.

Ultrastructure of meiosis and the spindle pole body cycle in freeze-substituted basidia of the smut fungi Ustilago maydis and Ustilago avenae

1992 ◽  
Vol 70 (3) ◽  
pp. 629-638 ◽  
Author(s):  
Kerry O'Donnell
Keyword(s):  
Electron Microscopy ◽  
Spindle Pole Body ◽  
Ustilago Maydis ◽  
Spindle Pole ◽  
Meiotic Spindle ◽  
Smut Fungi ◽  
Late Prophase ◽  
Prophase I ◽  
Pole Body ◽  
Middle Piece

Meiosis in the smut fungi Ustilago maydis and Ustilago avenae (Basidiomycota, Ustilaginales) was studied by electron microscopy of serial-sectioned freeze substituted basidia. At prophase I, a spindle pole body composed of two globular elements connected by a middle piece was attached to the extranuclear surface of each nucleus. Astral and spindle microtubules were initiated at each globular element at late prophase I to prometaphase I. During spindle initiation, the middle piece disappeared and interdigitating half-spindles entered the nucleoplasm, which was surrounded by discontinuous nuclear envelope together with perinuclear endoplasmic reticulum. Kinetochore pairs at metaphase I were analyzed to obtain a karyotype for each species. The meiotic spindle pole body replicational cycle is described. Key words: electron microscopy, freeze-substitution, meiosis, Ustilago, spindle pole body.

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

1999 ◽  
Vol 112 (14) ◽  
pp. 2313-2321 ◽  
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.

scholarly journals Novelsfi1Alleles Uncover Additional Functions for Sfi1p in Bipolar Spindle Assembly and Function

2007 ◽  
Vol 18 (6) ◽  
pp. 2047-2056 ◽  
Author(s):  
Victoria E. Anderson ◽  
John Prudden ◽  
Simon Prochnik ◽  
Thomas H. Giddings ◽  
Kevin G. Hardwick
Keyword(s):  
Essential Gene ◽  
Light And Electron Microscopy ◽  
Spindle Pole Body ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
The Novel ◽  
Synthetic Lethal ◽  
Bipolar Spindle ◽  
Novel Alleles ◽  
And Function

A variety of spindle and kinetochore defects have been shown to induce a mitotic delay through activation of the spindle checkpoint. With the aim of identifying novel mitotic defects we carried out a mad1 synthetic lethal screen in budding yeast. In this screen, four novel alleles of sfi1 were isolated. SFI1 is an essential gene, previously identified through its interaction with centrin/CDC31 and shown to be required for spindle pole body (SPB) duplication. The new mutations were all found in the C-terminal domain of Sfi1p, which has no known function, but it is well conserved among budding yeasts. Analysis of the novel sfi1 mutants, through a combination of light and electron microscopy, revealed duplicated SPBs <0.3 μm apart. Importantly, these SPBs have completed duplication, but they are not separated, suggesting a possible defect in splitting of the bridge. We discuss possible roles for Sfi1p in this step in bipolar spindle assembly.

scholarly journals The NIMA Kinase Is Required To Execute Stage-Specific Mitotic Functions after Initiation of Mitosis

2013 ◽  
Vol 13 (1) ◽  
pp. 99-109 ◽  
Author(s):  
Meera Govindaraghavan ◽  
Alisha A. Lad ◽  
Stephen A. Osmani
Keyword(s):  
Spindle Assembly Checkpoint ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Cycle Phase ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Content Type ◽  
Mitotic Entry ◽  
Spindle Pole Bodies ◽  
Pore Complexes

ABSTRACTThe G2-M transition inAspergillus nidulansrequires the NIMA kinase, the founding member of the Nek kinase family. Inactivation of NIMA results in a late G2arrest, while overexpression of NIMA is sufficient to promote mitotic events independently of cell cycle phase. Endogenously tagged NIMA-GFP has dynamic mitotic localizations appearing first at the spindle pole body and then at nuclear pore complexes before transitioning to within nuclei and the mitotic spindle and back at the spindle pole bodies at mitotic exit, suggesting that it functions sequentially at these locations. Since NIMA is indispensable for mitotic entry, it has been difficult to determine the requirement of NIMA for subaspects of mitosis. We show here that when NIMA is partially inactivated, although mitosis can be initiated, a proportion of cells fail to successfully generate two daughter nuclei. We further define the mitotic defects to show that normal NIMA function is required for the formation of a bipolar spindle, nuclear pore complex disassembly, completion of chromatin segregation, and the normal structural rearrangements of the nuclear envelope required to generate two nuclei from one. In the remaining population of cells that enter mitosis with inadequate NIMA, two daughter nuclei are generated in a manner dependent on the spindle assembly checkpoint, indicating highly penetrant defects in mitotic progression without sufficient NIMA activity. This study shows that NIMA is required not only for mitotic entry but also sequentially for successful completion of stage-specific mitotic events.

scholarly journals Reorientation of Mispositioned Spindles in Short Astral Microtubule Mutantspc72Δ Is Dependent on Spindle Pole Body Outer Plaque and Kar3 Motor Protein

2002 ◽  
Vol 13 (4) ◽  
pp. 1366-1380 ◽  
Author(s):  
Dominic Hoepfner ◽  
Florian Schaerer ◽  
Arndt Brachat ◽  
Achim Wach ◽  
Peter Philippsen
Keyword(s):  
Spindle Pole Body ◽  
Time Lapse ◽  
Nuclear Migration ◽  
Spindle Pole ◽  
Astral Microtubule ◽  
Spindle Pole Bodies ◽  
Microtubule Motor ◽  
Microtubule Formation ◽  
Mother Cells

Nuclear migration and positioning in Saccharomyces cerevisiae depend on long astral microtubules emanating from the spindle pole bodies (SPBs). Herein, we show by in vivo fluorescence microscopy that cells lacking Spc72, the SPB receptor of the cytoplasmic γ-tubulin complex, can only generate very short (<1 μm) and unstable astral microtubules. Consequently, nuclear migration to the bud neck and orientation of the anaphase spindle along the mother-bud axis are absent in these cells. However,SPC72 deletion is not lethal because elongated but misaligned spindles can frequently reorient in mother cells, permitting delayed but otherwise correct nuclear segregation. High-resolution time-lapse sequences revealed that this spindle reorientation was most likely accomplished by cortex interactions of the very short astral microtubules. In addition, a set of double mutants suggested that reorientation was dependent on the SPB outer plaque and the astral microtubule motor function of Kar3 but not Kip2/Kip3/Dhc1, or the cortex components Kar9/Num1. Our observations suggest that Spc72 is required for astral microtubule formation at the SPB half-bridge and for stabilization of astral microtubules at the SPB outer plaque. In addition, our data exclude involvement of Spc72 in spindle formation and elongation functions.

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.

Cytology and ultrastructure of Thanatephorus cucumeris and related taxa of the Rhizoctonia complex

1977 ◽  
Vol 55 (18) ◽  
pp. 2419-2436 ◽  
Author(s):  
C. C. Tu ◽  
James W. Kimbrough ◽  
H. C. Aldrich
Keyword(s):  
Electron Microscopy ◽  
Light Microscope ◽  
Light And Electron Microscopy ◽  
Middle Layer ◽  
Ultrastructural Level ◽  
Aniline Blue ◽  
Diploid Nucleus ◽  
Thanatephorus Cucumeris ◽  
Light Microscope Level ◽  
Endoplasmic Reticula

Cytological studies on the vegetative hyphae of members of the Rhizoctonia complex and basidial structures of Thanatephorus cucumeris were performed with light and electron microscopy. Vegetative cells of Thanatephorus and Waitea proved to be multinucleate, whereas those of Uthatobasidium, Ceratobasidium, Athelia. and Botryobasidium are binucleate.Dolipore septa of Thanatephorus, Waitea, Uthatobasidium, and Ceratobasidium are visible with the light microscope when stained with aniline blue in glycerine. Ultrastructurally, pore caps in these genera consisted of two-layered unit membranes, forming cisternae with an electron-dense middle layer. Dolipore septa of Athelia (S. rolfsii) and Botryobasidium are not visible in aniline blue at the light microscope level. At the ultrastructural level, there was an additional cisternal membrane making up a pore cap of three membranes. The fine structure of nuclei, mitochondria, endoplasmic reticula, vacuoles, and other organelles in the basidial structures of T. cucumeris was essentially the same as in other basidiomycetes.Karyogamy of two haploid nuclei occurs in the young basidia of T. cucumeris. The nuclear envelopes of both haploid nuclei break at their adjacent sides and fuse to form a diploid nucleus. After a short interphase, meiosis occurs. No leptotene was observed at prophase I, but a synaptinemal complex was evident and six pairs of chromosomes were observed throughout pachytene, diplotene, and diakinesis. The nuclear envelope disappears at metaphase I and a spindle appears. The second meiotic division is equational. Most of the mature and discharged spores are uninucleate.

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