Mitosis Spindle

Wadsworth, P. (1993). Mitosis spindle assembly and chromosome motion. Curr. Opin. Cell Biol. 5, 123-128. 

Jensen KG, Onfelt A, Wallin M (1991b) Effects of organotin compounds on mitosis, spindle structure, toxicity and in vitro microtubule assembly. Mutagenesis, 6(5) 409-416. 

During mitosis spindle fibers are extranuclear. During mitosis spindle fibers are endonuclear. During mitosis nuclear envelope partially differentiates. 

The mode of action has not yet been elucidated but the manufacturer states that it probably behaves like the herbicide triflurolin and its congeners. These materials inhibit cell division by binding to tubuHn thereby internipting micro-tubule development. This, in turn, stops spindle fiber formation essential to mitosis and cell division. Experiments with C-labeled Prime+ show that it is acutely toxic to fish with estimated LC q (96 h) of less than 100 ppb for rainbow trout and bluegiU. sunfish. However, channel catfish did not exhibit any toxic response at the maximum attainable water concentration (10). 

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. 

DCPA inhibits the growth of grass species by dismpting the mitotic sequence, probably at entry (190). DCPA influences spindle formation and function (181) and causes root-tip swelling (182) and britde shoot tissue (191). It has been reported that DCPA, like colchicine and vinblastine, attests mitosis at prometaphase and is associated with formation of polymorphic nuclei after mitotic arrest (192). Pronamide also inhibits root growth by dismpting the mitotic sequence in a manner similar to the effect of colchicine and the dinitroanilines (193,194). Cinmethylin and bensuhde prevent mitotic entry by unknown mechanisms (194). 

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

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. 

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. 

A signal transduction pathway required for proper chromosome alignment during mitosis. The spindle assembly checkpoint is activated during mitosis in response to the presence of chromosomes that are not attached to spindle microtubules or that are not properly aligned at the metaphase plate. The spindle checkpoint... 

Vinca alkaloids are derived from the Madagascar periwinkle plant, Catharanthus roseus. The main alkaloids are vincristine, vinblastine and vindesine. Vinca alkaloids are cell-cycle-specific agents and block cells in mitosis. This cellular activity is due to their ability to bind specifically to tubulin and to block the ability of the protein to polymerize into microtubules. This prevents spindle formation in mitosing cells and causes arrest at metaphase. Vinca alkaloids also inhibit other cellular activities that involve microtubules, such as leukocyte phagocytosis and chemotaxis as well as axonal transport in neurons. Side effects of the vinca alkaloids such as their neurotoxicity may be due to disruption of these functions. 

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... 

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... 

The vast majority of in vivo tests show no geno-toxicity of mono- and dialkyltins. Results from in vitro tests are variable, with little indication of DNA reactivity. There are, however, indications of clastogenicity and effects on spindle formation in mitosis in vitro. 

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. 

Epithelial cells express but do not apically localize Pins, and do not express Insc. We have previously shown that ectopically expressed Insc localizes to the apical cortex in wild-type epithelial cells (Kraut et al 1996). Interestingly, ectopic Insc expression causes Pins, which is normally localized to the lateral cortex, to localize to the apical cortex. Conversely, apical localization of ectopically expressed Insc is dependent on pins. Insc ectopically expressed in Pins- epithelial cells does not localize as an apical crescent it adopts a cytoplasmic distribution which is enriched towards the apical side of the cell during interphase and is undetectable during mitosis, presumably due to rapid degradation. This instability of ectopically expressed Insc may be why the 90° rotation in the mitotic spindles which occurs as a consequence of Insc ectopic expression in the wild-type epithelial cells no longer occurs when Insc is expressed in Pins-embryos. These results indicate that Insc is necessary and sufficient for the recruitment of Pins to the apical cortex of wild-type epithelial cells. 

Nurse I thought they were arguing that a first stage is formed which couldn t go any further with a cyclin A induced activity, and this would allow the spindle to orient before you got too far into mitosis. 

Newport I think that was what it was. Cyclin A stabilizes spindles. In this case, with low Cdc2 it was actually going through mitosis a little bit faster than normal, and the spindle itself might not have time to orient properly, or it might rock a bit. This would result in an asymmetric division. 

Hunt Normally cyclin A goes away very early in mitosis—almost as soon as the nuclear envelope breaks down. If it doesn t go away, what seems to happen is that the spindle doesn t organize itself properly, yet it goes through anaphase. It is peculiar the spindles look horrible. These are spindles with both cyclin A and cyclin B. The cyclin A seems to be necessary to get it up to that point, but then you need to get rid of it in order for the cyclin B to take over. 

Gonc y I have a question regarding spindle reorientation . Do you mean actual spindle reorientation, or rather centrosome repositioning prior to mitosis ... 

Chia It is actually spindle reorientation. It occurs during mitosis. The spindle actually sets up, and the whole thing rotates. 

Newport-. The way that spindles and microtubules are normally reoriented is by the stabilization of dynamic instability at the plus-end of the microtubule. So if microtubules were to embed in this apically localized complex, they would effectively be capped and this would reorient the spindle. One would expect that this would happen to the centriole prior to mitosis, so that the interphase microtubules would be stabilized at that location as well. Are you saying this doesn t happen If it doesn t happen, perhaps Cdc2 is necessary to activate this apical region for stabilizing plus ends, and this would explain why it rocks about. Are any of these molecules potential candidates for capping microtubules at the plus-end, for instance ... 

Sbrana I, Di Sibio A, Lomi A, Scarcelli V (1993) C-mitosis and numerical chromosome aberration analyses in human-lymphocytes - 10 known or suspected spindle poisons. Mutat Res 287 57-70 Senesi N, Loffredo E, Padovano G (1990) Effects of humic acid-herbicide interactions on the growth of Pisum sativum in nutrient solution. Plant Soil 127 41-47... 

DMT, TMT, DBT, TBT and DPhT chlorides exhibited in vitro spindle disturbance in V79 Chinese hamster cells of brain tubulin. The V79 cells lose stainable spindles at higher concentration. The cell mitosis activity effect at low concentration increased with the lipophilicity of the OTC, but all compounds showed a concentration dependence on microtubules. The OTC seem to act through two different cooperative mechanisms inhibition of microtubule assembly and interaction with hydrophobic sites. The latter mechanism might involve Cl/OH ion exchange28. 

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