Spindle Microtubules in the Dividing Nuclei of Trypanosomes

1970 ◽  
Vol 6 (2) ◽  
pp. 365-383 ◽  
Author(s):  
K. VICKERMAN ◽  
T. M. PRESTON
Keyword(s):  
Electron Microscope ◽  
Nuclear Envelope ◽  
Nuclear Division ◽  
Sleeping Sickness ◽  
Condensed Chromatin ◽  
Division Process ◽  
Spindle Microtubules

Stages in nuclear division have been identified in sections of bloodstream and cultured trypanosomes examined with the electron microscope. In the sleeping sickness trypanosome Trypanosoina rhodesiense at division the nuclear envelope and nucleolus-like endosome persist and become stretched along an axis. An acentric spindle of microtubules encases the elongating endosome As division proceeds the endosomal material fragments In bloodstream forms condensed chromatin (chromosomal material) appears to be associated with the nuclear envelope during the phase of nuclear elongation but to fall away from the envelope late in the phase of nuclear constriction. In culture forms the chromatin is not so abundant The discrete chromosomes envisaged by some light microscopists in stained preparations have not been identified using the electron microscope. The spindle may contain only continuous microtubules. It is suggested that the spindle serves to push the two halves of the nucleus apart, and that the nuclear envelope of each half may act as a vehicle in separation of the daughter genomes. In culture forms of the elasmobranch parasite T. raiae, the endosome appears to disintegrate as the spindle is formed, and from then onwards it becomes difficult to distinguish endosomal material from what might be chromatin. There is no noticeable association between chromatin-like material and the nuclear envelope. Some of the spindle tubules converge on kinetochore-like plaques and the presence of chromosomal microtubules cannot be ruled out. These preliminary studies indicate that the nuclear division process of trypanosomes is not closely akin to eukaryote mitosis, though it may bear some resemblance to nuclear division in Euglena. Within the genus Trypanosoma, moreover, the nuclear division process may vary from species to species and, possibly, even from one strain to another within a species.

Ultrastructural changes in nuclear membranes and organelle associations during mitosis of the aquatic fungus Entophlyctis sp.

1975 ◽  
Vol 53 (7) ◽  
pp. 627-646 ◽  
Author(s):  
Martha J. Powell
Keyword(s):  
Endoplasmic Reticulum ◽  
Nuclear Envelope ◽  
Nuclear Division ◽  
Ultrastructural Changes ◽  
Aquatic Fungus ◽  
Electron Microscopic ◽  
Mitotic Apparatus ◽  
Inner Membrane ◽  
Nuclear Membranes ◽  
Spindle Microtubules

Electron microscopic observations on an endobiotic chytrid, Entophlyctis sp., have revealed a mitotic apparatus which is presently unique among fungi. Daughter nuclear envelopes are reconstituted from cisternae apparently proliferated by the inner membrane of the nuclear envelope. Before nuclear division, centrioles replicate and migrate to the poles of the nucleus. Large pores appear at this time in a depression of the nuclear envelope opposite the paired centrioles. This region of the envelope fragments and leaves polar fenestrae as spindle microtubules appear in the nucleus. The inner membrane of the nuclear envelope then invaginates and proliferates cisternae until a layer of inner membrane cisternae lines the original nuclear envelope at late metaphase. Connections between the inner membrane of the original nuclear envelope and the cisternae persist until telophase. As the spindle elongates and the inner membrane cisternae fuse centripetally to form a reticulum around the chromatin mass, the original nuclear envelope opens more at the poles. The reticulum becomes the nuclear envelope of the new daughter nuclei. When the original envelope finally disperses, it is distinguishable from the endoplasmic reticulum only by the presence of pores. Microbodies are consistently associated with the original nuclear envelope and appear adjacent to the new daughter envelopes at the end of telophase. Densely staining arms project from the sides of the primary centrioles toward the polar mitochondria.

scholarly journals The ultrastructure and timing of events in the nuclear cycle of the fungus Entomophaga aulicae

1988 ◽  
Vol 90 (3) ◽  
pp. 501-516
Author(s):  
FAYE MURRIN ◽  
WILLIAM NEWCOMB ◽  
I. BRENT HEATH
Keyword(s):  
Nuclear Envelope ◽  
Linear Array ◽  
Nuclear Division ◽  
Metaphase Plate ◽  
Serial Sections ◽  
Free Zone ◽  
Nuclear Cycle ◽  
Full Complement ◽  
Spindle Microtubules ◽  
Spindle Elongation

The ultrastructure of the mitotic nuclear division cycle of the fungus Entomophaga aulicae was studied from serial sections of hyphal tips and protoplasts. The extranuclear bar-shaped nucleus- associated organelle (NAO) remained associated with the persistent nuclear envelope throughout. Prior to spindle formation, a patch of intranuclear NAO-associated chromatin detached from the nuclear envelope to yield a chromatin free zone containing fine filaments and a linear array of presumptive kinetochores. Early metaphase spindles less than 1μm in length were characterized by a ‘fused’ metaphase plate consisting of kinetochore-associated chromatin and a full complement of at least 15 kinetochore microtubules per half-spindle, while most of the chromatin was remote from the intranuclear spindle. Analysis of the distribution of antiparallel spindle microtubules indicated that polar separation and concomitant spindle elongation through metaphase were not accompanied by intermicrotubule sliding. Anaphase exhibited extensive decondensation of the large patches of condensed chromatin characteristic of all other stages. In a logarithmically growing protoplast population all nuclei contained spindle microtubules, with metaphase occupying approximately 66% of the nuclear cycle time. The calculated genome size of 4.3 pg, and average DNA content per chromosome of 0.3 pg, are extremely high for fungi.

Ultrastructure of Mitosis in the Aquatic Phycomycete Chytriomyces Hyalinus

1980 ◽  
Vol 38 ◽  
pp. 498-499
Author(s):  
David G. Pechak
Keyword(s):  
Life Cycle ◽  
Nuclear Envelope ◽  
Nuclear Division ◽  
Condensed Chromatin ◽  
Nuclear Pores ◽  
Interphase Nuclei ◽  
Aquatic Phycomycete ◽  
Simple Life

The aquatic Phycomycetes, particularly the Chytridiales, are a group of fungi with a rather simple life cycle and morphology. With the advent of ultrastructural investigations on these organisms, two stable characteristics (zoospore ultrastructure and nuclear division) have proven helpful in elucidating relationships in this perplexing taxon. The latter is described in this communication. Conventional techniques were employed in the preparation of the material. Interphase nuclei of C. hyalinus are essentially spherical in shape, measure approximately 2.8 μm in diameter, and have a single, centrally located, nucleus. Prophase nuclei, while not exhibiting condensed chromatin, are characterized by the presence of migrating centrioles and a fusiform or spindle-shape to the nuclear profile (Fig. 1). Nuclear pores predominate near the polar ends of the nuclear envelope. No evidence has been found to indicate that centrioles replicate during prophase.

Ultrastructure of the Fungal Nucleus

1971 ◽  
Vol 9 (2) ◽  
pp. 453-473
Author(s):  
M. GIRBARDT
Keyword(s):  
Nuclear Envelope ◽  
Direct Contact ◽  
Nuclear Division ◽  
Higher Plants ◽  
Compound Structure ◽  
Interphase Nuclei ◽  
Electron Dense Material ◽  
Nuclear Age ◽  
Division Process ◽  
Polar Organelle

The electron-dense material which regularly occurs at the poles of the nuclei of certain fungi during division has been studied in hyphal interphase nuclei of 4 basidio- and 3 ascomycetes. The shape of this material varies with the species and the nuclear age and may be that of a sphere or a dumbbell. In some instances paired diskoidal structures are found in the place of the globular elements of the dumbbell configuration. The organelle in question lies in an invagination of the nuclear envelope preferentially at the forward pointing pole of the nucleus. Its size (0.1-0.5 µm) is correlated with the size of the nucleus. In Polystictus versicolor the diameter of both globular elements of the polar organelle increases during initiation of the division process. The structure is identical with the fungal ‘centriole’ of light-microscopical studies but lacks the characteristic organization of a true centriole. It is suggested that the polar organelle is the equivalent of a kinetochore because it maintains continuous and direct contact with the nuclear envelope (on its cytoplasmic aspect), seems to be connected with the karyoplasm, exhibits oscillating movements, is continuous with microtubules during division and resembles in its fine structure the kinetochores of the chromosomes of higher plants and animals. In addition to its function as an organelle of nuclear motility it also seems to play a part in the initiation of DNA synthesis and nuclear division. If this is correct one would expect to find the genome of the fungal nucleus having the form of a unitary, coherent compound structure (chain) extending from or incorporating a single, solitary kinetochore.

Mitosis in Phlyctochytrium irregulare

1973 ◽  
Vol 51 (11) ◽  
pp. 2065-2074 ◽  
Author(s):  
Rand McNitt
Keyword(s):  
Endoplasmic Reticulum ◽  
Electron Microscope ◽  
Nuclear Envelope ◽  
Green Algae ◽  
Light Microscope ◽  
Equatorial Plate ◽  
Metaphase Chromosomes ◽  
Mitotic Apparatus ◽  
Initial Separation ◽  
Spindle Microtubules

Mitosis in zoosporangia of the chytrid Phlyctochytrium irregulare is described from electron microscope observations and also from light microscope observations of both living and haematoxylin-stained thalli. At the onset of prophase the centriole complex replicates, and the complexes migrate to polar positions. The semi-persistent nucleolus is appressed to the nuclear envelope as the nuclear pockets invaginate, finally rupturing to create polar fenestrae, through which spindle microtubules penetrate the nucleus from the region of the centrioles at prometaphase. Metaphase chromosomes form an equatorial plate. Initial separation at anaphase seems to be accomplished mainly by shortening of chromosome-to-pole microtubules; additional anaphase and telophase separation is accomplished by elongation of the nucleus. A system of perinuclear endoplasmic reticulum is formed during prophase and is completed by metaphase. It persists during all division stages after its formation. Features of this mitotic apparatus are discussed with reference to earlier light microscope studies of chytrid mitosis. The ultrastructure of P. irregulare's mitotic apparatus is similar to that of certain unicellular green algae.

The Ultrastructure of the Nuclear Events of Binary Fission in Paramecium bursaria and the Effects of Colchicine on Cell Division

1974 ◽  
Vol 32 ◽  
pp. 276-277
Author(s):  
L. M. Lewis
Keyword(s):  
Cell Division ◽  
Nuclear Envelope ◽  
Condensed Chromatin ◽  
Binary Fission ◽  
Paramecium Bursaria ◽  
Nuclear Events ◽  
Division Axis

The effects of colchicine on extranuclear microtubules associated with the macronucleus of Paramecium bursaria were studied to determine the possible role that these microtubules play in controlling the shape of the macronucleus. In the course of this study, the ultrastructure of the nuclear events of binary fission in control cells was also studied.During interphase in control cells, the micronucleus contains randomly distributed clumps of condensed chromatin and microtubular fragments. Throughout mitosis the nuclear envelope remains intact. During micronuclear prophase, cup-shaped microfilamentous structures appear that are filled with condensing chromatin. Microtubules are also present and are parallel to the division axis.

scholarly journals The Endoplasmic Reticulum and the Golgi Structures in Maize Root Cells

1959 ◽  
Vol 5 (3) ◽  
pp. 501-506 ◽  
Author(s):  
W. Gordon Whaley ◽  
Hilton H. Mollenhauer ◽  
Joyce E. Kephart
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Electron Microscope ◽  
Nuclear Envelope ◽  
Epoxy Resin ◽  
Maize Root ◽  
Root Tips ◽  
Animal Cells ◽  
Root Cells ◽  
Vesicular Structure

Maize root tips were fixed in potassium permanganate, embedded in epoxy resin, sectioned to show silver interference color, and studied with the electron microscope. All the cells were seen to contain an endoplasmic reticulum and apparently independent Golgi structures. The endoplasmic reticulum is demonstrated as a membrane-bounded, vesicular structure comparable in many aspects to that of several types of animal cells. With the treatment used here the membranes appear smooth surfaced. The endoplasmic reticulum is continuous with the nuclear envelope and, by contact at least, with structures passing through the cell wall. The nuclear envelope is characterized by discontinuities, as previously reported for animal cells. The reticula of adjacent cells seem to be in contact at or through the plasmodesmata. Because of these contacts the endoplasmic reticulum of a given cell appears to be part of an intercellular system. The Golgi structures appear as stacks of platelet-vesicles which apparently may, under certain conditions, produce small vesicles around their edges. Their form changes markedly with development of the cell.

scholarly journals STUDIES ON NUCLEI USING CORRELATED CYTOCHEMICAL, LIGHT, AND ELECTRON MICROSCOPE TECHNIQUES

1956 ◽  
Vol 2 (4) ◽  
pp. 397-406 ◽  
Author(s):  
Montrose J. Moses
Keyword(s):  
Electron Microscope ◽  
Nuclear Envelope ◽  
Light Microscope ◽  
Primary Spermatocyte ◽  
Feulgen Reaction ◽  
Remarkable Feature ◽  
Pas Reaction ◽  
Electron Image ◽  
Careful Comparison ◽  
Positive Nature

In this paper, a procedure for correlating electron microscope and light microscope cytochemical studies using immediately adjacent serial thin and thick sections has been described and discussed. This technique, combined with the Feulgen reaction for DNA, has been of particular value in framing and answering both general and specific questions about the nucleus. The results may be summarized as follows:— Apparent nuclear homogeneity in the electron microscope is not due to loss of DNA as evidenced by positive Feulgen reactions in such nuclei. Arrangement of Feulgen-positive material in chromosomes, heterochromatin, perinuclear and perinucleolar chromatin, etc., is similar to that customarily observed in the light microscope but this is not necessarily reflected in a cursory survey of the electron image. Careful comparison of light and electron images shows that fine differences in structure are associated with chromatin localization. Primary spermatocyte prophase chromosomes of crayfish have been positively identified by their Feulgen-positive nature. Core-like axial structures in such chromosomes have been observed (9) and are described further. A remarkable feature of spermiogenesis in the crayfish is an elaboration of the nuclear envelope of the spermatid accompanying the formation of what becomes a mass of convoluted membranes in the sperm. In the spermatid, perinuclear chromatin follows outpocketings of the nuclear envelope into the cytoplasm. In the early sperm, on the other hand, although the nuclear envelope is continuous with the system of convoluted membranes, the chromatin is distinct from it and is retained in the nucleus proper by some mechanism independent of the nuclear envelope. None of the above observations was apparent from the electron microscope images alone; they were possible only by virtue of the correlated cytochemical and electron microscope study of adjacent sections. The successful use of other cytochemical tests, such as the PAS reaction for certain carbohydrates, in such correlated studies is also described.

An Electron-Microscope Study of the Intranucleolar Chromatin in Root Meristematic Cells of Allium Cepa

1974 ◽  
Vol 15 (3) ◽  
pp. 645-657
Author(s):  
L. A. CHOUINARD
Keyword(s):  
Electron Microscope ◽  
Allium Cepa ◽  
Current Knowledge ◽  
General Concept ◽  
Condensed Chromatin ◽  
Condensed State ◽  
Interphase Cell ◽  
Gradual Process ◽  
Nucleolar Chromosome ◽  
Chromatin Material

The various states of condensation and configuration of the chromatin material, contained inside the lacunar regions of the interphase nucleolus in Allium cepa, have been investigated by means of conventional electron-microscope techniques. The observations reveal that in a number of lacunar profiles, the chromatin material in question appears in an extended state only; in other lacunar profiles of the same or different nucleoli, the chromatin material is present both in an extended and a condensed condition. Moreover, in some lacunar profiles, a single mass of chromatin in a condensed state is observed; in others, several discrete and often seemingly interconnected masses of condensed chromatin are visualized. An attempt is made to interpret these morphological findings in the light of current knowledge concerning the structural relationship of the nucleolar organizing segment of the nucleolar chromosome with the interphase nucleolus in plant cells. The relevant observational evidence would be consistent with the view that the chromatin-containing lacunar regions of the interphase nucleolus in Allium cepa correspond, in fact, to cross or oblique sections of a meandering channel through which the nucleolar organizing segment of the nucleolar chromosome passes. Assuming the applicability to intranucleolar chromatin of the general concept of condensed-inactive versus extended-active chromatin, it is hypothesized that the various states of condensation of intralacunar chromatin merely reflect variations in the functional activity of the nucleolar organizing segment during the interphase cell cycle in the species investigated. With regard to variations in the configurational state of the intralacunar condensed chromatin, it is postulated that they are the cytological expression of the gradual process of coiling or folding upon itself of the nucleolar organizing segment during late interphase and in preparation for the next mitosis.

Sign in / Sign up

Export Citation Format

Share Document