Spindles, mitotic

The influences of herbicides on cell division fall into two classes, ie, dismption of the mitotic sequence and inhibition of mitotic entry from interphase (G, S, G2). If ceU-cycle analyses indicate increases in abnormal mitotic figures, combined with decreases in one or more of the normal mitotic stages, the effect is upon mitosis. Mitotic effects usually involve the microtubules of the spindle apparatus in the form of spindle depolymerization, blocked tubulin synthesis, or inhibited microtubule polymerization (163). Alkaloids such as colchicine [64-86-8J,viahla.stiae [865-21-4] and vincristine [57-22-7] dismpt microtubule function (164). Colchicine prevents microtubule formation and promotes disassembly of those already present. Vinblastine and vincristine also bind to free tubulin molecules, precipitating crystalline tubulin in the cytoplasm. The capacities of these dmgs to interfere with mitotic spindles, blocking cell division, makes them useful in cancer treatment. 

Certain proteins endow cells with unique capabilities for movement. Cell division, muscle contraction, and cell motility represent some of the ways in which cells execute motion. The contractile and motile proteins underlying these motions share a common property they are filamentous or polymerize to form filaments. Examples include actin and myosin, the filamentous proteins forming the contractile systems of cells, and tubulin, the major component of microtubules (the filaments involved in the mitotic spindle of cell division as well as in flagella and cilia). Another class of proteins involved in movement includes dynein and kinesin, so-called motor proteins that drive the movement of vesicles, granules, and organelles along microtubules serving as established cytoskeletal tracks. ... 

Some are mitosis inhibitors which affect microtubule function and hence the formation of the mitotic spindle, others are topoisomerase I and II inhibitors. 

In contrast to the DNA damage checkpoint, the mitotic spindle checkpoint is essential for cell viability. Dierefore, targeting kinases of the spindle checkpoint including Bubl, BubRl, and Mpsl might be a valid strategy for anticancer treatment. 

Centrosomes, also called the microtubule organizing centre, are protein complexes that contain two cen-trioles (ringlike structures) and y- tubulin. They serve as nucleation points for microtubular polymerization and constrain the lattice structure of a microtubule to 13 protofilaments. They are responsible for organizing the mitotic spindle during mitosis. 

Karsenti E, Vernos I (2001) The mitotic spindle a self-made machine. Science 294 543-547... 

Mayer TU, Kapoor TM, Haggarty SJ et al (1999) Small molecule inhibitor of mitotic spindle bipolarity identified in a phenotype-based screen. Science 286 971... 

The phase of the cell cycle where the sister chromatids are separated and distributed onto two daughter nuclei. First, upon entry into mitosis the chromosomes are condensed followed by the breakdown of the nuclear-envelope (prophase). The two centrosomes are separated and induce the formation of the mitotic spindle. Then, the chromosomes are captures by the spindle and aligned on the metaphase plate (metaphase). The sister-chromatids are separated and pulled to the poles of the spindle (anaphase). In telophase, two new nuclei are formed around the separated chromatids. 

Tubulin is a major component of the cellular cytoskele-ton. Tubulin polymers (microtubules) are important for cell division (mitotic spindle) and the chemotaxis and phagocytosis of neutrophils. Prevention of tubulin polymerisation by colchicine accounts for the therapeutic effects of this drug in acute gouty arthritis and its anti-mitotic effects. 

Role of the Cytoskeleton in Cell Division Formation of the Mitotic Spindle, Mitosis, and Cytokinesis Drug Effects on Microtubules Mlcrofllaments Actin Filaments Structure and Composition... 

Radial arrays are best exemplified by mitotic half-spindles, which have a central MTOC, the centrosome. The centrosome consists of two centrioles (which are homologous with the basal body) surrounded by dense pericentriolar material (Kalt and Schliwa, 1993). In plant cells, the MTOC of the mitotic spindle consists of dense material only without centrioles. The plus ends of microtubules of the mitotic spindle are directed toward the equator of the cell. Some are free, and others attach to kinetochores on chromatids (see Figure 4). 

Cytokinesis (cell division) in animal cells involves the progressive formation in telophase of a furrow between the two daughter cells in the equator of the mitotic spindle. Immunofluorescent staining of the cortical cytoplasm at the site of the contraction ring reveals an abundance of actin as well as myosin, a-actinin, and filamin (Fishkind and Wang, 1995). Cytokinesis is highly sensitive to actin-myosin inhibitors such as cytochalasin and phalloidin. 

In terms of evolutionary biology, the complex mitotic process of higher animals and plants has evolved through a progression of steps from simple prokaryotic fission sequences. In prokaryotic cells, the two copies of replicated chromosomes become attached to specialized regions of the cell membrane and are separated by the slow intrusion of the membrane between them. In many primitive eukaryotes, the nuclear membrane participates in a similar process and remains intact the spindle microtubules are extranuclear but may indent the nuclear membrane to form parallel channels. In yeasts and diatoms, the nuclear membrane also remains intact, an intranuclear polar spindle forms and attaches at each pole to the nuclear envelope, and a single kinetochore microtubule moves each chromosome to a pole. In the cells of higher animals and plants, the mitotic spindle starts to form outside of the nucleus, the nuclear envelope breaks down, and the spindle microtubules are captured by chromosomes (Kubai, 1975 Heath, 1980 Alberts et al., 1989). 

Several groups of drugs that bind to tubulin at different sites interfere with its polymerization into microtubules. These drugs are of experimental and clinical importance (Bershadsky and Vasiliev, 1988). For example, colchicine, an alkaloid derived from the meadow saffron plant Colchicum autumnale or Colchicum speciosum), is the oldest and most widely studied of these drugs. It forms a molecular complex with tubulin in the cytosol pool and prevents its polymerization into microtubules. Other substances such as colcemid, podophyllotoxin, and noco-dazole bind to the tubulin molecule at the same site as colchicine and produce a similar effect, albeit with some kinetic differences. Mature ciliary microtubules are resistant to colchicine, whereas those of the mitotic spindle are very sensitive. Colchicine and colcemid block cell division in metaphase and are widely used in cytogenetic studies of cultured cells to enhance the yield of metaphase plate chromosomes. 

Cytokinesis begins with astral relaxation of the cell cortex, perhaps triggered by the mitotic spindle, followed by the accumulation in a circumferential equatorial band of actin filaments and associated myosin molecules to form a contractile... 

Mitchison, T.J. (1989). Polewards microtubule flux in the mitotic spindle Evidence from photoactivation of fluorescence. J. Cell Biol. 109, 637-652. 

Microtubule-Based Motor Proteins The Meiotic and Mitotic Spindles Microfilament-Based Intracellular Motility Cytokinesis... 

The processes of meiosis and mitosis involve many motile events, from the separation of the daughter chromosomes to the final act of cell separation at cytokinesis (Wadsworth, 1993). DNA replication itself may be considered as a motile event, because the polymerase complex moves along the linear DNA. One of the most obvious motile events is the separation of the chromosomes along the mitotic spindle at anaphase. Details of the structure and polarity of microtubules in the spindle apparatus in meiosis and mitosis are known through electron and light microscopy, but it is not yet clear whether the chromosomes are pushed, pulled or... 

Fujiwara, K., Pollard, T.D. (1976). Fluorescent antibody localization of myosin in the cytoplasm, cleavage furrow and mitotic spindle of human cells. J. Cell Biol. 71, 848-875. 

It is possible to observe effects of organotin(lV) compounds exposure such as inhibition of cleavage of fertilized eggs, interference with the formation of the mitotic spindle, damages affecting chromosome structure, and electron-dense precipitate formation in organelles. 

Microtubules, an integral component of the cellular cy-toskeleton, consist of cytoplasmic tubes 25 nm in diameter and often of extreme length. Microtubules are necessary for the formation and function of the mitotic spindle and thus are present in all eukaryotic cells. They are also involved in the intracellular movement of endocytic and exocytic vesicles and form the major structural components of cilia and flagella. Microtubules are a major component of axons and dendrites, in which they maintain structure and participate in the axoplasmic flow of material along these neuronal processes. 

Fig. 2.3 The development of polarity and asymmetric division in Saccharomyces cerevisiae. The diagram is reproduced in a slightly simplified form from the work of Lew Reed (1995) with the permission of Current Opinion in Genetics and Development, (a) The F-actin cytoskeleton strands = actin cables ( ) cortical actin patches, (b) The polarity of growth is indicated by the direction of the arrows (arrows in many directions signifies isotropic growth), (c) 10-nm filaments which are assembled to form a ring at the neck between mother and bud. (d) Construction of the cap at the pre-bud site. Notice that the proteins of the cap become dispersed at the apical/isotropic switch, first over the whole surface of the bud, then more widely. Finally, secretion becomes refocussed at the neck in time for cytokinesis, (e) The status and distribution of the nucleus and microtubules of the spindle. Notice how the spindle pole body ( ) plays an important part in orientation of the mitotic spindle.

Colchicine has a long history of successful use and was the treatment of choice for many years. It is used infrequently today because of its low therapeutic index. Colchicine is thought to exert its anti-inflammatory effects by interfering with the function of mitotic spindles in neutrophils by binding of tubulin dimers this inhibits phagocytic activity. 

Available as a 0.5% gel or solution containing purified extract of the most active compound of podophyllin Arrests the formation of the mitotic spindle, prevents cell division, and may also induce damage in blood vessels within the warts... 

Mailer Our hypothesis is that CSF is at the kinetochore. George Vande Woude published some data showing that the kinetochore protein CENP-E has certain masked epitopes only in a CSF-arrested spindle and not in a mitotic spindle. 

Mailer Why do you say that the first spindle poles are made of PCM Is there some reason to think that PCM is needed without a centrosome In Nenopus, I have never heard anyone argue that there is PCM organizing the meiotic spindles. If you look at the /-tubulin staining pattern, it is totally different in a meiotic spindle than in a mitotic spindle. 

Kalab P, Pu RT, Dasso M 1999 The ran GTPase regulates mitotic spindle assembly. Curr Biol 9 481-484... 

FIG. 2. Sister chromatid separation does not depend on the mitotic spindle. Light micrographs of mitosis in living flattened endosperm from Haemanthus katherinae BAK. treated with colchicine (c-mitosis). The micrographs were taken at 10 min intervals. Size bar, 10 /tm. Reprinted with permission from Mole-Bajer (1958). 

The chromatid separation process has also remained mysterious. It is an autonomous process that does not direcdy depend on the mitotic spindle (Wilson 1925, Mazia 1961). This is most vividly seen in cells whose spindles have been destroyed by spindle poisons such as colchicine. In many organisms, in particular in plant cells, the cell cycle delay induced by colchicine is only transient and chromatids eventually split apart in the complete absence of a mitotic spindle (Mole-Bajer 1958, Rieder Palazzo 1992) (Fig. 2). Mitosis in the presence of colchicine or colcemid (known as c-mitosis) leads to the production of daughter cells with twice the normal complement of chromosomes. This process is routinely used for manipulating plant genomes and may contribute to the therapeutic effects of taxol in treating breast cancer. 

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