Metaphase

Metaphase analysis or microiuidc-us assay in rodent bone marrow... 

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Parasorbic acid (Figure 2) was isolated from fruits of Sorbus aucuparia. Germination of mustard seed Sinapis alba) was affected adversely by parasorbic acid at 3.5 X 10-3 M and growth of excised tomato roots was inhibited at approximately 8.5 X 10 4 M (25). The acid also antagonized indoleacetic acid (IAA) in the Avena assay. Cornman 29,30) reported that parasorbic acid slowed down mitosis. Metaphase stages were observed to accumulate, but abnormalities were not detected. 

Protoanemonin, which has been isolated from Anemone pulsatilla and Ranunculus spp., was reported to inhibit root growth by slowing down metabolism and blocking mitosis 35). Erickson and Rosen 35) observed cytological effects in corn root tips at concentrations of 10M and lower. Cells undergoing division appeared to accumulate in the interphase or prophase stages. Metaphase, anaphase, and telophase stages were not observed. Cytoplasmic and vacuolar structures were disturbed and the presence of mitochondria could not be demonstrated in treated tissue. Thimann and Bonner 141) reported that protoanemonin was 10 to 30 times more inhibitory than coumarin in coleoptile and split pea stem tests, and that BAL prevented the inhibitory action. 

Vinca alkaloids (vincristine, vinblastine, vindesine) are derived from the periwinkle plant (Vinca rosea), they bind to tubulin and inhibit its polymerization into microtubules and spindle formation, thus producing metaphase arrest. They are cell cycle specific and interfere also with other cellular activities that involve microtubules, such as leukocyte phagocytosis, chemotaxis, and axonal transport in neurons. Vincristine is mainly neurotoxic and mildly hematotoxic, vinblastine is myelosuppressive with veiy low neurotoxicity whereas vindesine has both, moderate myelotoxicity and neurotoxicity. 

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. 

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. 

Gorbsky, G.J. Borisy, G.G. (1989). Microtubules of the kinetochore fiber turn over in metaphase but not in anaphase. J. Cell Biol. 109, 653-662. 

Rat bone marrow cells Aberrant metaphases + Dikshith et al. 1978... 

Mouse bone marrow Aberrant metaphases + L Vova 1984... 

In vitro metaphase analysis (or mouse micronucleus test)... 

Figure 36-3. Shown is the extent of DNA packaging in metaphase chromosomes (fop) to noted dupiex DNA (bottom). Chromosomai DNA is packaged and organized at severai ieveis as shown (seeTabie 36-2), Each phase of condensation or compaction and organization (bottom to top) decreases overaii DNA accessibiiity to an extent that the DNA sequences in metaphase chromosomes are aimost totaiiy transcriptionaiiy inert, in toto, these five ieveis of DNA compaction resuit in neariy a 10 -foid iinear decrease in end-to-end DNA iength. Compiete condensation and decondensation of the iinear DNA in chromosomes occur in the space of hours during the normai repiicative ceii cycie (see Figure 36-20).

At metaphase, mammalian chromosomes possess a twofold symmetry, with the identical duplicated sister chromatids connected at a centromere, the relative po-... 

Figure 36-6. A human karyotype (of a man with a normal 46,XY constitution), in which the metaphase chromosomes have been stained by the Giemsa method and aligned according to the Paris Convention. (Courtesy of H Lawce and F Conte.)...

Figure 36-9. The process of crossing-over between homologous metaphase chromosomes to generate recombinant chromosomes. See also Figure 36-12.

Lewis, C.D. and Laemmli, U.K. (1982). Higher order metaphase chromosome structure evidence for metal-loprotein interactions. Cell 29, 171-181. 

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