Microtubule-organizing centres and assembly of the double-spiral microtubule pattern in certain heliozoan axonemes

1981 ◽  
Vol 50 (1) ◽  
pp. 259-280
Author(s):  
J.C. Jones ◽  
J.B. Tucker
Keyword(s):  
Nuclear Envelope ◽  
Surface Membrane ◽  
Cold Treatment ◽  
Dense Material ◽  
Microtubule Assembly ◽  
Central Nucleus ◽  
Spiral Pattern ◽  
Microtubule Organizing Centres ◽  
Double Spiral ◽  
Actinophrys Sol

The double-spiral microtubule pattern is established by a self-linkage procedure when axopodial axonemes reassemble after cold treatment in multinucleate Echinosphaerium nucleofilum and mononucleate Actinophrys sol. Nuclei are related spatially to axoneme morphogenesis in both organisms but in rather different ways. Microtubules grow out in all directions from discrete clumps of dense material situated close to nuclei in E. nucleofilum as axonemal assembly begins. Each clump acts as a microtubule-organizing centre (MTOC) in so far as it is associated spatially with the assembly of microtubules for a single axoneme. The dense material spreads along the sides of a developing axoneme for several micrometers, where it probably promotes further microtubule assembly as the double-spiral pattern is established. Pattern is generated as microtubules that are randomly oriented to begin with become more closely juxtaposed and aligned with each other. There are indications that juxtaposition is brought about by the contractile action of a filamentous meshwork that interconnects the microtubules. Final positioning and alignment appears to be accomplished by a ‘zippering’ together of adjacent portions of microtubules that proceeds in both directions along the lengths of developing axonemes as self-linkage is effected. Considerable numbers of more or less radially oriented microtubules remain and project from the surface membrane of the single central nucleus during cold treatment of A. sol. Additional tubules assemble and become associated similarly with the nuclear envelope immediately after cold treatment. Initially these microtubules are not arranged in a double-spiral pattern, which is subsequently generated by procedures similar to those outlined above for E. nucleofilum. It is suggested that the surface of the nuclear envelope may act as an MTOC.

scholarly journals From the herringbone dome by Sangallo to the Serlio floor of Emy (and beyond)

2021 ◽  
Vol 8 (1) ◽  
pp. 259-270
Author(s):  
Giulio Mirabella Roberti ◽  
Giuseppe Ruscica ◽  
Vittorio Paris
Keyword(s):  
Thin Shells ◽  
Spiral Pattern ◽  
Structural Scheme ◽  
Wooden Floor ◽  
Construction Stage ◽  
Structural Role ◽  
Double Spiral ◽  
The Cross ◽  
Structural Solutions ◽  
Geometrical Relationship

Abstract The research starts from an analogy found between two apparently very different structural solutions: the double spiral pattern of the herringbone brick courses in the domes built by Antonio da Sangallo the Younger (1484-1546) during the Renaissance, and the particular pattern of a wooden floor ‘à la Serlio’, described by Amand Rose Emy in his Treatise at the beginning of 19th century, made by diagonal beams reciprocally sustained. The diagonal pattern of the floor has a geometrical relationship with the cross-herringbone pattern, so that the latter can be obtained by some geometrical transformations of the former. This pattern was also used in thin shells built by Nervi, from the destroyed airplane hangars in Tuscany to the Palazzetto dello sport in Rome, and even by Piacentini in 1936 and earlier in some neoclassical domes. Thus the construction tool, useful for building domes without expensive scaffolding, could have a structural role at the completed construction stage. Within the research different structures were investigated, in order to observe the relevance of this peculiar structural scheme particularly in the construction of modern domes.

scholarly journals Chromosomes initiate spindle assembly upon experimental dissolution of the nuclear envelope in grasshopper spermatocytes.

1995 ◽  
Vol 131 (5) ◽  
pp. 1125-1131 ◽  
Author(s):  
D Zhang ◽  
R B Nicklas
Keyword(s):  
Nuclear Envelope ◽  
Essential Role ◽  
Spindle Assembly ◽  
Microtubule Assembly ◽  
Chromosomal Protein ◽  
Spindle Microtubule ◽  
Late Prophase ◽  
Spindle Formation ◽  
Bipolar Spindle

Chromosomes are known to enhance spindle microtubule assembly in grasshopper spermatocytes, which suggested to us that chromosomes might play an essential role in the initiation of spindle formation. Chromosomes might, for example, activate other spindle components such as centrosomes and tubulin subunits upon the breakdown of the nuclear envelope. We tested this possibility in living grasshopper spermatocytes. We ruptured the nuclear envelope during prophase, which prematurely exposed the centrosomes to chromosomes and nuclear sap. Spindle assembly was promptly initiated. In contrast, assembly of the spindle was completely inhibited if the nucleus was mechanically removed from a late prophase cell. Other experiments showed that the trigger for spindle assembly is associated with the chromosomes; other constituents of the nucleus cannot initiate spindle assembly in the absence of the chromosomes. The initiation of spindle assembly required centrosomes as well as chromosomes. Extracting centrosomes from late prophase cells completely inhibited spindle assembly after dissolution of the nuclear envelope. We conclude that the normal formation of a bipolar spindle in grasshopper spermatocytes is regulated by chromosomes. A possible explanation is an activator, perhaps a chromosomal protein (Yeo, J.-P., F. Alderuccio, and B.-H. Toh. 1994a. Nature (Lond.). 367: 288-291), that promotes and stabilizes the assembly of astral microtubules and thus promotes assembly of the spindle.

scholarly journals Alp7-Mto1 and Alp14 synergize to promote interphase microtubule regrowth from the nuclear envelope

2019 ◽  
Vol 11 (11) ◽  
pp. 944-955 ◽  
Author(s):  
Wenyue Liu ◽  
Fan Zheng ◽  
Yucai Wang ◽  
Chuanhai Fu
Keyword(s):  
Nuclear Envelope ◽  
Schizosaccharomyces Pombe ◽  
Fission Yeast ◽  
Microtubule Assembly ◽  
Dependent Manner ◽  
Microtubule Nucleation ◽  
Microtubule Organizing Centers ◽  
Evolutionarily Conserved ◽  
Microtubule Growth ◽  
In Cells

Abstract Microtubules grow not only from the centrosome but also from various noncentrosomal microtubule-organizing centers (MTOCs), including the nuclear envelope (NE) and pre-existing microtubules. The evolutionarily conserved proteins Mto1/CDK5RAP2 and Alp14/TOG/XMAP215 have been shown to be involved in promoting microtubule nucleation. However, it has remained elusive as to how the microtubule nucleation promoting factors are specified to various noncentrosomal MTOCs, particularly the NE, and how these proteins coordinate to organize microtubule assembly. Here, we demonstrate that in the fission yeast Schizosaccharomyces pombe, efficient interphase microtubule growth from the NE requires Alp7/TACC, Alp14/TOG/XMAP215, and Mto1/CDK5RAP2. The absence of Alp7, Alp14, or Mto1 compromises microtubule regrowth on the NE in cells undergoing microtubule repolymerization. We further demonstrate that Alp7 and Mto1 interdependently localize to the NE in cells without microtubules and that Alp14 localizes to the NE in an Alp7 and Mto1-dependent manner. Tethering Mto1 to the NE in cells lacking Alp7 partially restores microtubule number and the efficiency of microtubule generation from the NE. Hence, our study delineates that Alp7, Alp14, and Mto1 work in concert to regulate interphase microtubule regrowth on the NE.

scholarly journals Role of spindle microtubules in the control of cell cycle timing.

1979 ◽  
Vol 80 (3) ◽  
pp. 674-691 ◽  
Author(s):  
G Sluder
Keyword(s):  
Cell Cycle ◽  
Nuclear Envelope ◽  
Sea Urchin ◽  
Control Cell ◽  
Microtubule Assembly ◽  
Nuclear Envelope Breakdown ◽  
Anaphase Onset ◽  
Spindle Cells ◽  
Spindle Microtubules

Sea urchin eggs are used to investigate the involvement of spindle microtubules in the mechanisms that control the timing of cell cycle events. Eggs are treated for 4 min with Colcemid at prophase of the first mitosis. No microtubules are assembled for at least 3 h, and the eggs do not divide. These eggs show repeated cycles of nuclear envelope breakdown (NEB) and nuclear envelope reformation (NER). Mitosis (NEB to NER) is twice as long in Colcemid-treated eggs as in the untreated controls. Interphase (NER to NEB) is the same in both. Thus, each cycle is prolonged entirely in mitosis. The chromosomes of treated eggs condense and eventually split into separate chromatids which do not move apart. This "canaphase" splitting is substantially delayed relative to anaphase onset in the control eggs. Treated eggs are irradiated after NEB with 366-nm light to inactivate the Colcemid. This allows the eggs to assemble normal spindles and divide. Up to 14 min after NEB, delays in the start of microtubule assembly give equal delays in anaphase onset, cleavage, and the events of the following cell cycle. Regardless of the delay, anaphase follows irradiation by the normal prometaphase duration. The quantity of spindle microtubules also influences the timing of mitotic events. Short Colcemid treatments administered in prophase of second division cause eggs to assemble small spindles. One blastomere is irradiated after NEB to provide a control cell with a normal-sized spindle. Cells with diminished spindles always initiate anaphase later than their controls. Telophase events are correspondingly delayed. This work demonstrates that spindle microtubules are involved in the mechanisms that control the time when the cell will initiate anaphase, finish mitosis, and start the next cell cycle.

scholarly journals Intracellular growth of some viruses of the pox group. An electron microscopic study of infected chick chorionic cells

1956 ◽  
Vol 54 (3) ◽  
pp. 393-400 ◽  
Author(s):  
T. H. Flewett
Keyword(s):  
Vaccinia Virus ◽  
Microscopic Study ◽  
Electron Microscopic Study ◽  
Surface Membrane ◽  
Central Nucleus ◽  
Intracellular Growth ◽  
Electron Microscopic ◽  
Virus Growth ◽  
In Cells

Sections of chorio-allantoic membranes fixed at intervals after infection with large doses of vaccinia virus showed almost homogeneous areas appearing in the cytoplasm after 4 hr.; these areas contained immature forms of virus which had a thin surface membrane and an eccentric ‘nucleoid’, and were surrounded by mitochondria. Mature forms of virus, having a larger central nucleus-like structure and a thicker cortex, were first found in areas of virus growth 10 hr. after inoculation. Similar immature and mature forms were found in cells infected with fowl-pox, myxomatosis and ectromelia viruses. It is concluded that the immature forms are of low infectivity or not infective.

scholarly journals Spindle microtubule differentiation and deployment during micronuclear mitosis in Paramecium.

1985 ◽  
Vol 101 (5) ◽  
pp. 1966-1976 ◽  
Author(s):  
J B Tucker ◽  
S A Mathews ◽  
K A Hendry ◽  
J B Mackie ◽  
D L Roche
Keyword(s):  
Nuclear Envelope ◽  
Early Stage ◽  
Microtubule Assembly ◽  
Membrane Association ◽  
Paramecium Tetraurelia ◽  
Spindle Microtubule ◽  
Spatial Control ◽  
Spindle Microtubules ◽  
Spindle Elongation ◽  
Anaphase B

Spindles underwent a 12-fold elongation before anaphase B was completed during the closed mitoses of micronuclei in Paramecium tetraurelia. Two main classes of spindle microtubules have been identified. A peripheral sheath of microtubules with diameters of 27-32 nm was found to be associated with the nuclear envelope and confined to the midportion of each spindle. Most of the other microtubules had diameters of approximately 24 nm and were present along the entire lengths of spindles. Nearly all of the 24-nm microtubules were eliminated from spindle midportions (largely because of microtubule disassembly) at a relatively early stage of spindle elongation. Disassembly of some of these microtubules also occurred at the ends of spindles. About 60% of the total microtubule content of spindles was lost at this stage. Most, perhaps all, peripheral sheath microtubules remained intact. Many of them detached from the nuclear envelope and regrouped to form a compact microtubule bundle in the spindle midportion. There was little, if any, further polymerization of 24-nm microtubules after the disassembly phase. Polymerization of microtubules with diameters of 27-32 nm continued as spindle elongation progressed. Most microtubules in the midportions of well-elongated spindles were constructed from 14-16 protofilaments. A few 24-nm microtubules with 13 protofilaments were also present. The implications of these findings for spatial control of microtubule assembly, disassembly, positioning, and membrane association, that apparently discriminate between microtubules with different protofilament numbers have been explored. The possibility that microtubule sliding occurs during spindle elongation has also been considered.

scholarly journals ELECTRON MICROSCOPY OF BASOPHILIC STRUCTURES OF SOME INVERTEBRATE OOCYTES

1956 ◽  
Vol 2 (1) ◽  
pp. 93-104 ◽  
Author(s):  
Lionel I. Rebhun
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Nuclear Envelope ◽  
Cross Sections ◽  
Dense Material ◽  
Continuous Space ◽  
Surf Clam ◽  
Surface View ◽  
Hexagonal Pattern

Highly basophilic plate-shaped regions from oocytes of the surf clam have been examined with the electron microscope. The regions are composed of flat, hollow vesicles perforated by pores arranged, in surface view, in a hexagonal pattern. Cross-sections of this structure show a periodicity consisting of loops (cross-sections of the continuous space within the vesicle) alternating with spaces partly filled with dense material (pores). These structures are shown to resemble closely, the nuclear envelope. Similarities to and differences from basophilic regions of other cells are discussed and it is suggested that the small granules of Palade (38) are represented by granules composing the walls of the annuli of the nuclear envelope and assumed to be present in the annuli of the vesicles. Because of differences in the structure of these regions from basophilic regions of other cells, the name periodic lamellae is suggested since the structures show periodically repeating substructures (annuli) in both cross-sections and surface views.

Identification of a spindle-associated protein in ciliate micronuclei

1989 ◽  
Vol 93 (2) ◽  
pp. 287-298
Author(s):  
GUY KERYER ◽  
NICOLE GARREAU DE LOUBRESSE ◽  
NICOLE BORDES ◽  
MICHEL BORNENS
Keyword(s):  
Cell Cycle ◽  
Monoclonal Antibody ◽  
Nuclear Envelope ◽  
Mammalian Cells ◽  
Fibrous Material ◽  
Cortical Microtubule ◽  
Ciliated Protozoa ◽  
Paramecium Tetraurelia ◽  
Electron Microscope Level ◽  
Microtubule Organizing Centres

Ciliated protozoa display a nuclear dualism, with germinal micronuciei and a somatic macronucleus. During mitosis, which proceeds without disruption of the nuclear envelope, a spindle is organized within the micronucleus from, presumably, intranuclear microtubule-organizing centres (MTOCs). In order to characterize these MTOCs, monoclonal antibodies generated against human centrosomes were screened on several ciliates and particularly on Paramecium tetraurelia. In this ciliate, the monoclonal antibody CTR 532, which decorates centrosomal and spindle-associated components in mammalian cells, specifically labelled the micronuclei during interphase. At the electron-microscope level, it stained a fibrous material surrounding microtubules localized on the inner face of the nuclear envelope. During mitosis this decoration extended all over the metaphase spindle. At all stages of the cell cycle, the decoration remained specific to the micronucleus and was absent not only from all of the various cytoplasmic and cortical microtubule arrays but also from the macronuclei, even at early stages of their development from the zygotic nucleus. CTR 532 recognizes a single 170x103 Mr polypeptide in the cytoskeletal fraction that contains micronuclei and this polypeptide is absent in the cytoskeletal fraction of amicronucleate cells.

scholarly journals A temperature-sensitive NUP116 null mutant forms a nuclear envelope seal over the yeast nuclear pore complex thereby blocking nucleocytoplasmic traffic.

1993 ◽  
Vol 123 (2) ◽  
pp. 275-284 ◽  
Author(s):  
S R Wente ◽  
G Blobel
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Pore Complex ◽  
Nuclear Periphery ◽  
Dense Material ◽  
Nuclear Pore ◽  
Temperature Sensitive ◽  
Electron Microscopic ◽  
Electron Dense Material ◽  
Cytoplasmic Face ◽  
Delta Cells

NUP116 encodes a 116-kD yeast nuclear pore complex (NPC) protein that is not essential but its deletion (nup116 delta) slows cell growth at 23 degrees C and is lethal at 37 degrees C (Wente, S. R., M. P. Rout, and G. Blobel. 1992. J. Cell Biol. 119:705-723). Electron microscopic analysis of nup116 delta cells shifted to growth at 37 degrees C revealed striking perturbations of the nuclear envelope: a double membrane seal that was continuous with the inner and outer nuclear membranes had formed over the cytoplasmic face of the NPCs. Electron-dense material was observed accumulating between the cytoplasmic face of these NPCs and the membrane seal, resulting in "herniations" of the nuclear envelope around individual NPCs. In situ hybridization with poly(dT) probes showed the accumulation of polyadenylated RNA in the nuclei of arrested nup116 delta cells, sometimes in the form of punctate patches at the nuclear periphery. This is consistent with the electron microscopically observed accumulation of electron-dense material within the nuclear envelope herniations. We propose that nup116 delta NPCs remain competent for export, but that the formation of the membrane seals over the NPCs blocks nucleocytoplasmic traffic.

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