scholarly journals THE FINE STRUCTURE OF MITOSIS IN RAT THYMIC LYMPHOCYTES

1965 ◽  
Vol 26 (2) ◽  
pp. 601-619 ◽  
Author(s):  
Raymond G. Murray ◽  
Assia S. Murray ◽  
Anthony Pizzo
Keyword(s):  
Plasma Membrane ◽  
Fine Structure ◽  
Nuclear Envelope ◽  
Early Prophase ◽  
Late Prophase ◽  
Daughter Cells ◽  
Central Plate ◽  
Spindle Apparatus ◽  
Late Telophase

The fine structure of rat thymic lymphocytes from early prophase to late telophase of mitosis is described, using material fixed at pH 7.3 either in 1 per cent OsO4 or in glutaraldehyde followed by 2 per cent OsO4. The structure of the centriolar complex of interphase thymocytes is analyzed and compared with that of centrioles during division. The appearance of daughter centrioles is the earliest clearly recognizable sign of prophase. Daughter centrioles probably retain a secondary relation to the primary centriole, while the latter appears to be related, both genetically and spatially, to the spindle apparatus. The nuclear envelope persists in recognizable form to help reconstitute the envelopes of the daughter nuclei. Ribosome bodies (dense aggregates of ribosomes) accumulate, beginning at late prophase, and are retained by the daughter cells. Cytokinesis proceeds by formation of a ribosome-free plate at the equator with a central plate of vesicles which may coalesce to form the new plasma membrane of the daughter cells. Stages in the formation of the midbody are illustrated.

Nucleolus behaviour during the cell cycle of a primitive dinoflagellate eukaryote, Prorocentrum micans Ehr., seen by light microscopy and electron microscopy

1992 ◽  
Vol 102 (3) ◽  
pp. 475-485 ◽  
Author(s):  
MARIE-ODILE SOYER-GOBILLARD ◽  
MARIE-LINE GERAUD
Keyword(s):  
Cell Cycle ◽  
Light Microscopy ◽  
Early Prophase ◽  
Microscopy Observation ◽  
Prorocentrum Micans ◽  
Late Prophase ◽  
Daughter Cells ◽  
Nucleolar Material ◽  
Freeze Fixation ◽  
Higher Eukaryotes

Light-microscopy observation of the dinoflagellate Prorocentrum micans after silver-staining of the argyrophilic proteins of the nucleolar organizing region (Ag-NOR staining) showed the presence of nucleolar material throughout the vegetative cell cycle, and in particular during all the mitotic stages. This contrasts with the case in most higher eukaryotes, in which nucleoli disappear at the end of prophase and are reconstituted in daughter cells during telophase. Electron-microscope (EM) observations after conventional or fast-freeze fixation revealed that during interphase several functional nucleoli with three compartments (NORs, the fibrillogranular and the preribosomal granular compartments) are present in a nucleus in which the envelope is persistent and the chromosomes are always compact. During early prophase, when chromosomes are beginning to split, the nucleoli remain functional, whereas in late prophase they contain only a NOR and the granular component, and the chromosomes are surrounded by many protein masses. In early telophase, the nucleolar material coating the chromosomes migrates along with the chromosomes. Nucleologenesis occurs through the formation of prenucleolar bodies around lateral or telomeric nucleofilaments extruding from the chromosomes. Several chromosomes can contribute to the formation of one nucleolus. The behaviour of these ‘persistent nucleoli’ in a closed-nucleus model such as that of the dinoflagellates is discussed with regard to the higher eukaryotes.

scholarly journals Human Cyclin a Is Required for Mitosis until Mid Prophase

1999 ◽  
Vol 147 (2) ◽  
pp. 295-306 ◽  
Author(s):  
Nobuaki Furuno ◽  
Nicole den Elzen ◽  
Jonathon Pines
Keyword(s):  
Cyclin A ◽  
Time Lapse ◽  
S Phase ◽  
Early Prophase ◽  
Cyclin Dependent Kinase ◽  
Late Prophase ◽  
Daughter Cells ◽  
G2 Phase ◽  
Rate Limiting

We have used microinjection and time-lapse video microscopy to study the role of cyclin A in mitosis. We have injected purified, active cyclin A/cyclin-dependent kinase 2 (CDK2) into synchronized cells at specific points in the cell cycle and assayed its effect on cell division. We find that cyclin A/CDK2 will drive G2 phase cells into mitosis within 30 min of microinjection, up to 4 h before control cells enter mitosis. Often this premature mitosis is abnormal; the chromosomes do not completely condense and daughter cells fuse. Remarkably, microinjecting cyclin A/CDK2 into S phase cells has no effect on progress through the following G2 phase or mitosis. In complementary experiments we have microinjected the amino terminus of p21Cip1/Waf1/Sdi1 (p21N) into cells to inhibit cyclin A/CDK2 activity. We find that p21N will prevent S phase or G2 phase cells from entering mitosis, and will cause early prophase cells to return to interphase. These results suggest that cyclin A/CDK2 is a rate-limiting component required for entry into mitosis, and for progress through mitosis until late prophase. They also suggest that cyclin A/CDK2 may be the target of the recently described prophase checkpoint.

Location of the HIV-1 Rev protein during mitosis: inactivation of the nuclear export signal alters the pathway for postmitotic reentry into nucleoli

1996 ◽  
Vol 109 (9) ◽  
pp. 2239-2251 ◽  
Author(s):  
M. Dundr ◽  
G.H. Leno ◽  
N. Lewis ◽  
D. Rekosh ◽  
M.L. Hammarskjoid ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Export ◽  
Nuclear Export Signal ◽  
Nucleolar Protein ◽  
Early Prophase ◽  
Nucleolar Proteins ◽  
Late Telophase ◽  
Export Signal ◽  
Hiv 1 ◽  
Rev Protein

The HIV-1 Rev protein localizes predominantly to the nucleolus of HIV-1-infected or Rev-expressing cells. The subcellular location of Rev during mitotic nucleolar disintegration was examined at various stages of mitosis in synchronized Rev-expressing CMT3 cells. During early prophase Rev was predominantly located in disintegrating nucleoli and began to accumulate at the peripheral regions of chromosomes in late prophase, eventually distributing uniformly on all chromosomes in prometaphase. In anaphase Rev remained associated with the perichromosomal regions, but significant amounts of Rev were also seen in numerous nucleolus-derived foci. The movement of Rev from disintegrating nucleoli to perichromosomal regions and foci was similar to that of nonribosomal nucleolar proteins, including fibrillarin, nucleolin, protein B23 and p52 of the granular component. During telophase Rev remained associated with perichromosomal regions and mitotic foci until the nuclear envelope started to reform. When nuclear envelope formation was complete in late telophase, nonribosomal nucleolar proteins were present in prenucleolar bodies (PNBs) which were eventually incorporated into nucleoli; at the same time, Rev was excluded from nuclei. In contrast, a trans-dominant negative Rev protein containing an inactive nuclear export signal reentered nuclei by the nonribosomal nucleolar protein pathway in late telophase, associating with PNBs and reformed nucleoli. Rev protein reentry into postmitotic nuclei was delayed until early G1 phase, but before the arrival of ribosomal protein S6. Thus, Rev behaves like a nonribosomal nucleolar protein through mitosis until early telophase; however, its nuclear reentry seems to require reestablishment of both a nuclear import system and active nucleoli.

Mitosis and cell division in Cryptomonas (Cryptophyceae)

1977 ◽  
Vol 55 (22) ◽  
pp. 2789-2800 ◽  
Author(s):  
Berl R. Oakley ◽  
Thana Bisalputra
Keyword(s):  
Plasma Membrane ◽  
Cell Division ◽  
Nuclear Envelope ◽  
Red Algae ◽  
Amorphous Material ◽  
Solid Plate ◽  
Late Telophase

Mitosis and cytokinesis are examined in Cryptomonas sp., a member of the Cryptophyceae. The beginning of prophase is signalled by the replication of the flagellar bases which are at the anterior of the cell and a proliferation of the microtubules which run from them to the nucleus at the posterior. The microtubules continue to proliferate as the flagellar bases migrate apart and the nucleus migrates to the anterior. They dissociate from the flagellar bases and enter the nucleus as the nuclear envelope breaks down. A rectangular spindle forms and at prometaphase chromatin is scattered along the spindle. From this stage until late telophase microtubules are found attached singly to the chromatin. In metaphase the chromatin forms a solid plate penetrated by tunnels through which microtubules pass and in anaphase the chromatin separates in two masses which move toward the poles as the spindle elongates. In telophase the nuclear envelope re-forms while a number of microtubules remain between the daughter nuclei. The cytokinetic furrow forms during metaphase and constricts gradually until cytokinesis is complete at telophase. A thin ringof amorphous material is seen under the plasma membrane in the cytokinetic furrow. These results suggest that on the basis of mitotic criteria there is little similarity between the cryptophytes and either the dinoflagellates or red algae to which they have been previously linked.

scholarly journals Identification of a Golgi-associated protein that undergoes mitosis dependent phosphorylation and relocation.

1990 ◽  
Vol 110 (5) ◽  
pp. 1513-1523 ◽  
Author(s):  
I McMorrow ◽  
W E Souter ◽  
G Plopper ◽  
B Burke
Keyword(s):  
Monoclonal Antibody ◽  
Nuclear Envelope ◽  
Immunofluorescence Microscopy ◽  
Nuclear Lamina ◽  
Early Prophase ◽  
Perinuclear Region ◽  
Nuclear Envelope Breakdown ◽  
Peripheral Membrane Protein ◽  
Double Label ◽  
Late Telophase

By means of a monoclonal antibody (BH3), we have identified a 57-kD protein (p57) that in interphase is restricted largely to the perinuclear region of the cell. Double label immunofluorescence microscopy suggests localization of p57 to the Golgi complex and associated membranous structures. Protease protection experiments and chemical extractability indicate that p57 is a peripheral membrane protein exposed to the cytoplasm. p57 displays unique behavior during mitosis. At the end of G2 or in early prophase, p57 leaves the perinuclear region and accumulates very rapidly within the nucleus, at a time when the nuclear envelope is still intact and before nuclear lamina disassembly. This relocation of p57 coincides with its hyperphosphorylation on serine and threonine residues. After nuclear envelope breakdown p57 becomes uniformly distributed throughout the mitotic cytoplasm until in late telophase when it returns to its perinuclear location and is once again excluded from the nucleus. The behavior of p57 during mitosis suggests that it may play a role in the cellular reorganization evident during mitotic prophase.

scholarly journals UNE FORME MICROTUBULAIRE ET PARACRISTALLINE DE RETICULUM ENDOPLASMIQUE DANS LES PHOTOCYTES DES ANNELIDES POLYNOINÆ

1966 ◽  
Vol 31 (1) ◽  
pp. 135-158 ◽  
Author(s):  
J. M. Bassot
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Fine Structure ◽  
Nuclear Envelope ◽  
Contact Surface ◽  
Special Kind ◽  
The Other ◽  
Cytoplasmic Organelle ◽  
Specialized Form

Luminous cells of polynoid worm elytra have been examined by methods of electron microscopy, with special attention focused on the fine structure of photogenic grains. These cells send apical prolongations into the mid-part of the elytra. The plasma membrane is very sinuous, and a special kind of desmosome links two portions of the same membrane. In addition to all the organelles which can be found in nonluminescent epithelial cells of the elytra, numerous photogenic grains are contained in their cytoplasm. These grains are composed of undulating microtubules measuring 200 A in diameter; their disposition in the grain is highly regular, and the grains appear as paracrystals. At the borders of the grains, the walls of the microtubules are often in continuity with those of the endoplasmic reticulum and with the external membrane of the nuclear envelope. Because of this fact, the microtubules of the grains may be considered a cytoplasmic organelle, representing a specialized form of the endoplasmic reticulum. The microtubules permit the repartition, inside and outside their walls, of two different products, one being forty-three times more abundant than the other; thus, the contact surface, in comparison to the volume, is greatly increased. The induction of the luminous reaction by change in the permeability of the microtubule walls, allowing contact between the two substances, is suggested as a working hypothesis. There is an evolution of the grains along the axis of the photocytes. The grains are often surrounded by progressively increasing amounts of glycogen. Their paracrystalline disposition is altered at the apex of the luminous cells.

The fine structure of the flagellate Mixotricha paradoxa and its associated micro-organisms

1964 ◽  
Vol 159 (977) ◽  
pp. 668-686 ◽  
Keyword(s):  
Plasma Membrane ◽  
Fine Structure ◽  
Cell Surface ◽  
Nuclear Envelope ◽  
Internal Structure ◽  
Body Surface ◽  
The Body ◽  
Fine Structures ◽  
Micro Organisms ◽  
Extracellular Bacterium

Mixotricha is a large polymastigote flagellate from the gut of the termite Mastotermes darwiniensis . Its behaviour and fine structure are described in detail. A study of the method of locomotion, using cinematography, has shown that the four flagella are used not to propel the organism but to steer it; movements are brought about by the co-ordinated undulations of many thousands of spirochaetes which cover most of the body surface. The spirochaetes are attached to small brackets, of complex internal structure, which arise in rows from the cell surface. In addition to one or more spirochaetes, each bracket is also associated with an extracellular bacterium. The fine structures of both spirochaetes and bacteria are described. A network of fibrous strands lies immediately below the cell surface, each of its meshes being associated with one of the over-lying brackets. The cytoplasm contains great numbers of vacuoles, as well as dictyosomes and rough-surfaced membranes. The membranes forming these structures, as well as the membranes of the nuclear envelope and the plasma membrane, are all triple-layered but differ in dimensions and appearance. The rough-surfaced membranes are always associated with intra­-cellular bacteria. The taxonomic position of Mixotricha is discussed in the light of the findings on its structure and behaviour.

scholarly journals LE COMPLEXE MEMBRANAIRE SUPERFICIEL ET SON EVOLUTION LORS DE L'ELABORATION DES INDIVIDUS-FILS CHEZ TOXOPLASMA GONDII

1969 ◽  
Vol 43 (2) ◽  
pp. 329-342 ◽  
Author(s):  
Emile Vivier ◽  
André Petitprez
Keyword(s):  
Plasma Membrane ◽  
Fine Structure ◽  
Electron Microscope ◽  
Toxoplasma Gondii ◽  
Outer Membrane ◽  
Molecular Architecture ◽  
Daughter Cells ◽  
Membrane Complex ◽  
Local Differentiation

The parasitic protozoan Toxoplasma gondii has been examined with the electron microscope in order to study the fine structure and the formation of the membranes surrounding the cell. The study of the ultrastructure of the membranes covering the parasite shows the existence of a three-membraned complex. Only the outer membrane is considered to be the plasma membrane; the two membranes below it form an inseparable whole of changeable molecular architecture (modifications in appearance depending on the methods of fixation, local differentiation). During reproduction, which takes place by fission or more often by endogeny, the membranes of the daughter individuals are formed from the membranes of the parent. At first the middle and inner membranes of the parent extend, separating the cytoplasm of the daughter cells from that of the parent. The three-membrane complex of the endozoites is completed at the time of their liberation; the external membrane of the parent covers the leaving endozoites; thus, the plasma membrane of the daughter cells derives also from that of the parent. These findings on the origin and role of limiting membranes during reproduction differ entirely from those described so far for other cells.

A mutation in the spindle checkpoint arresting meiosis II in Brachiaria ruziziensis

Genome ◽  
2003 ◽  
Vol 46 (4) ◽  
pp. 724-728 ◽  
Author(s):  
Claudicéia Risso-Pascotto ◽  
Maria Suely Pagliarini ◽  
Cacilda Borges do Valle
Keyword(s):  
Nuclear Envelope ◽  
Spindle Checkpoint ◽  
Low Frequency ◽  
Early Prophase ◽  
Late Prophase ◽  
Brachiaria Ruziziensis ◽  
Sister Chromatids ◽  
Wide Range

Cytological characterization of BRA005568 accession of Brachiaria ruziziensis (2n = 2x = 18) showed a totally unexpected high frequency of abnormal meiotic products, from triads to hexads, and also tetrads with micro nuclei or microcytes. Meiosis I had a low frequency of abnormalities, mainly related to the chiasma terminalization process. In meiosis II, however, frequency of abnormalities increased exceptionally. Early prophase II was normal with the chromosome set enclosed by the nuclear envelope. However, in late prophase II, owing to the breakdown of the nuclear envelope, the chromosomes were scattered in the cytoplasm. Some chromosomes did not reach the metaphase II plate and remained scattered. The behavior of sister cells was inconsistent. While in one cell the chromosomes were totally aligned at the metaphase II plate, in the other they could be found completely scattered, leading to an asynchronous cell division. Cells with scattered chromosomes were unable to progress in meiosis. Thus, anaphase II failed to occur and sister chromatids were not released. Cells with non-aligned chromosomes in the metaphase II plate did not receive the "go ahead" sign to initiate anaphase II. Consequently, the scattered chromosomes produced telophase II nuclei of different sizes in situ. The asynchronous behavior led to the formation of a wide range of meiotic products. Results suggest that the present accession contains a mutation affecting the spindle checkpoint that arrests the second meiotic division.Key words: Brachiaria ruziziensis, meiosis II, microsporogenesis, mutation, spindle checkpoint.

Fine structure of the spermatozoon of Proteocephalus longicollis (Cestoda proteocephalidea)

1978 ◽  
Vol 36 (2) ◽  
pp. 572-573
Author(s):  
Z. Swiderski ◽  
R. D. Eklu-Natey
Keyword(s):  
Plasma Membrane ◽  
Fine Structure ◽  
Nuclear Envelope ◽  
Anterior Part ◽  
Shaped Cell ◽  
Total Lack ◽  
Cytoplasmic Microtubules ◽  
Unusual Finding

The spermatozoon of the proteocephalid cestode Proteocephalus longicollis (Zeder, 1800) is a very elongate, thread-shaped cell, about 300 μ m long and 0, 1 - 0, 9 pm in diameter, with no differentiation into head, midpiece and tail.The spermatozoon body (Figs. A-K) consists of: (a) two axonemes of the unique “9+1“ pattern, (b) an elongate nucleus, (c) numerous electron-dense, glycogen-like granules of different sizes and shapes and (d) cortical, cytoplasmic microtubules associated with the limiting plasma membrane. The total lack of acrosome and mitochondria is a remarkable and unusual finding which seems to be characteristic for all cestode spermatozoa examined so far.The nucleus of the spermatozoon, narrow and rod-shaped in its anterior part, becomes progressively enlarged and flattened toward the posterior end. The nuclear envelope is relatively thick and composed of two wavy membranes (Figs. G and H). The nucleoplasm is very loose and consists of fine filaments and granules of chromatin.

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