Prophase division

Caution is warranted when collecting cell cycle kinetic data if the effect is on mitosis. If cells contain numerous chromosomes, an accumulation of cells with chromosomes in the blocked metaphase configuration (clumped chromosomes) may be interpreted as an accumulation of prophase division figures. 

Figure 7. Prophase division figure in a cotton lateral root treated with an aqueous...

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. 

Phosphorylation also plays an evident part in cell division. Specifically, cytoskeleton-associated protein 2 (CKAP2) has a phosphorylation site at threonine 596. This threonine has been tracked and gets phosphorylated between prophase and metaphase, and dephosphorylated a short time later before anaphase, suggesting that the protein is phosphorylated during the formation of mitotic spindles. ... 

The first cell division of meiosis occurs in the primary oocyte but the process is arrested during prophase and remains so until puberty. Just before ovulation, meiosis, which has been arrested since before birth, resumes. The first division halves the number of chromosomes to produce the haploid secondary oocyte. The process is the same as that in spermatozoa (Chapter 20 see Figure 20.29 ) except that the two resulting haploid daughter cells are unequal in size. One is the large functional secondary oocyte whereas the other is much smaller and is known as the first polar body. The second meiotic division is arrested at metaphase. It is completed only at fertilisation. Once again, the division is unequal. One cell is large, the secondary oocyte. The other is small, a second polar body, which is discarded. 

This reduction is achieved through meiosis, a process in which two successive ceU divisions occur without intervening DNA duplication. As with the cell cycle, DNA duphcation wiU have aheady taken place prior to the cell division, so that during the initial prophase each pair of identical DNA molecules forms a pair of chromatids attached to each other at a centrosome. In contrast to mitosis, however, homologous chromosomes now pair up (metaphase I). Note that in a pair of homologous chromosomes each wiU contain the same genes (one of the pair having come from the mother and one from the father) but many of the alleles wiU be different. 

After the DNA is replicated during prophase of the first meiotic division, the resulting sister chromatids remain associated at their centromeres. At this stage, each set of four homologous chromosomes exists as two pairs of chromatids. Genetic information is now exchanged between the closely associated homologous chromatids... 

The distribution of chromosomes to daughter cells of somatic cells undergoing division is accomplished by mitosis whose successive phases are referred to as prophase, metaphase, anaphase, and telophase... 

During the prophase of the first meiotic division (meiosis I) two homologous pairs of partially "condensed" chromosomes must find each other and pair with appropriate orientation. A protein in the telomeres of the chromosomes seems to be involved.269 277 The key structure in meiotic crossing-over is the ribbonlike synaptonemal complex formed by the pairs of homologous chroma fids.271/278 2791 This complex, in which a proteinaceous core or axial element separates the greatly extended chromatid pairs (Fig. 26-13), is fully formed in the pachytene stage of meiosis. Formation of the synaptonemal complex is preceded by development of a few double-stranded breaks in... 

Fig. 3. Schematic illustrations of distinct steps in cell division show the central role of contractile motor action in the process of mitosis. (A) to (C) replication (prophase) (D) formation of the mitotic spindle (metaphase) (E) and (F) chromosome migration (anaphase) and building of the nuclear envelopes, and (G) formation of the contractile ring containing actin and myosin, forming the cleavage furrow and eventually two separate daughter cells. CE, centriole pair A, aster of microtubules N, nucleus M, microtubules C, chromosomes K, kinetochore NR, remnant of nuclear envelope NE, nucelar envelope reforming CR, contractile ring CM, cell membrane]. From Squire (1986).

Paclitaxel and docetaxel have been shown to act as spindle poisons, causing cell division cycle arrest, based on a unique mechanism of action.7-10 These drugs bind to the P-subunit of the tubulin heterodimer, the key constituent protein of cellular microtubules (spindles). The binding of these drugs accelerates the tubulin polymerization, but at the same time stabilizes the resultant microtubules, thereby inhibiting their depolymerization. The inhibition of microtubule depolymerization between the prophase and anaphase of mitosis results in the arrest of the cell division cycle, which eventually leads to the apoptosis of cancer cells. 

The nuclear division process during the M phase lasts less than an hour. The M phase can be divided into six distinct stages, according to the progression of nuclear division (prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis) (adapted from Alberts etal., 2002). 

G2 ends as the first of the five stages of cell division, prophase, begins. Prophase is defined as the first appearance of condensed chromosomes. This is followed by metaphase, in which spindle fibers appear leading from centromeres to opposite sides, or poles, of the cells. The sister chromosomes (i.e., the pairs formed by replication of single chromosomes in S) become aligned in one plane... 

Celldivision in eukaryotic cells is divided into division of the nucleus, mitosis, and division of the cell, C5n okinesis. Mitosis continues from the early prophase to the late telophase, when cytokinesis begins. 

For most cell types, mitosis typically lasts for less than Ih, and can be divided into prophase (chromosome condensation, growth of mitotic spindle and breakdown of nuclear envelope), metaphase (alignment of chromosomes along the equator of the parent cell), anaphase (separation of chromosomes) and telophase (formation of new nuclear membrane around chromosomes). Finally, furrowing and division of the cell takes place during cytokinesis to yield two distinct daughter cells. 

Richmond and Phillips (1975) found in the case of Botrytis cinerea that the conidia of the fungi produced distorted germ tubes in the presence of benomyl. In most of the fungi, cell division differed from classical mitosis, the normal states of which were not seen clearly in any of the treated material. Chromosomes became visible at the prophase-metaphase, but they did not completely separate. Finally, the chromatin became stretched into long threads, daughter nuclei did not separate completely and chromatin was often present as irregular shaped masses. 

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