Cell cycle Mitotic phase

Antineoplastic plant alkaloid cell cycle (M phase)-specific agent inhibits mitotic spindle formation. Tox peripheral neuropathy. Vinblastine, a congener, causes myelosuppression. 

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. 

The very beginning of the first mitotic cell cycle of the mouse embryo seems to be controlled by the mechanisms characteristic for both meiotic and mitotic cell cycles. Active MAP kinase, its substrate p90rsk and the CSF activity itself could influence the cellular processes within the one-cell embryo. Indeed, we have observed that despite the entry into the interphase (as judged by the low activity of MPF) some proteins are actively phosphorylated as during the meiotic M phase (e.g. 35 kDa complex Howlett et al 1986, Szollosi et al 1993), the nuclei and the microtubule interphase network start to form only 1.5 hours after activation (Szollosi et al 1993). This delay in the phenomena characteristic for the interphase could be linked to the mixed meiotic/mitotic character of this early period. This delay probably allows the correct transformation of the sperm nucleus into the male pronucleus. In species like Xenopus or Drosophila the transitional period between the meiotic and the mitotic cell cycle control is probably much shorter since it is proportional to duration of the short first cell cycle of these rapidly cleaving embryos. Mammalian embryos are perhaps the most suitable to study this transition because of the exceptionally long first embryonic cell cycle. 

The entry into the first mitotic M phase at the end of the first embryonic cell cycle requires activation of MPF. In the mouse one-cell embryo this activation is fully autonomous from the nucleus (Ciemerych 1995, Ciemerych et al 1998). It proceeds within the cytoplasts obtained either by enucleation or by bisection of the embryo. Other autonomous phenomena are the cortical activity, or the deformation of the one-cell embryo, directly preceding the entry into first mitosis (Waksmundzka et al 1984) and the cyclic activity of K+ ion channels (Day et al 1998). The role of the cortical activity remains unknown however, the fact that it directly precedes the entry into the first mitotic M phase suggests that it could be linked to the activation... 

However, in interphase delaminating neuroblasts, which are known to have completed S-phase and are at the G2 stage of the cell cycle, this codependence of Baz/Insc/Pins seen in mitotic neuroblasts does not apply. Delaminating neuroblasts possess an apical membrane stalk which retains contact with the epithelial surface and this is where apical cortical localization of Insc is initially seen (see Fig. 2). This initial localization of Insc to the apical stalk occurs... 

The cell cycle is a key process that recurs in a periodic manner. Early cell cycles in amphibian embryos are driven by a mitotic oscillator. This oscillator produces the repetitive activation of the cyclin-dependent kinase cdkl, also known as cdc2 [131]. Cyclin synthesis is sufficient to drive repetitive cell division cycles in amphibian embryonic cells [132]. The period of these relatively simple cell cycles is of the order of 30 min. In somatic cells the cell cycle becomes longer, with durations of up to 24 h or more, owing to the presence of checkpoints that ensure that a cell cycle phase is properly completed before the cell progresses to the next phase. The cell cycle goes successively through the phases Gl, S (DNA replication), G2, and M (mitosis) before a new cycle starts in Gl. After mitosis cells can also enter a quiescent phase GO, from which they enter Gl under mitogenic stimulation. 

Vincristine and vinblastine are generally considered to act specifically on the metaphase portion of the mitotic (M) stage of the cell cycle as a consequence of perturbations of the structure and function of tubulin. A characteristic action of the drugs is production of mitotic arrest in which the tJercentage of cells in mitosis in a given population of cells will rise from a few percent to 50% and more after treatment with a drug such as vinblastine. There are reports, however, that these drugs can interfere with other phases of the cell cycle in ways not clearly related to interference with tubulin function (5). 

The vinca alkaloids bind avidly to tubulin, a class of proteins that form the mitotic spindle during cell division. The drugs cause cellular arrest in metaphase during mitosis, and cell division cannot be completed. Although the vinca alkaloids usually have been regarded as phase specific in the cell cycle, some mammalian cells are most vulnerable in the late S-phase. 

Fig. 8 illustrates how increasing LET reduces the differences in radiosensitivity related to the position of the cells in the mitotic cycle [31]. Cells in stationary phase and in S phase are significantly more radio-resistant than mitotic cells. 

Dividing hydrogenosomes can be found in all phases of the trichomonads cell cycle, similar to mitochondria (Suzuki et al. 1994). They were even observed during the mitotic process (Benchimol and Engelke 2003). During the inter-... 

The simultaneous measurement of BrdU incorporation and DNA content confers sensitivity and versatility in detection of cell cycle perturbations in response drugs or radiation and tracing the lineage of a cell within the cell cycle. The use of computer-generated windows facilitates the analysis of any population of cells within any phase of the cell cycle and is not restricted to the mitotic window, as is the case with 3HTdR/autoradiography. 

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