Cell cycle Mitosis

Kaposi s sarcoma-associated herpesvirus Bcl-2 homolog low molar mass DNA cell cycle mitosis phase... 

BRD4 H4K5, K12 Cell cycle/mitosis, viral gene... 

The eukaryotic somatic cell cycle is defined by a sequential order of tasks a dividing cell has to complete it must replicate its DNA, segregate its chromosomes, grow, and divide. The cell cycle can be divided into four discrete phases. DNA replication is restricted to S phase (DNA synthesis phase), which is preceded by a gap phase called G1 and followed by a gap phase called G2. During mitosis (M phase) the sister chromatids are segregated into two new daughter nuclei and mitosis is completed by the division of the cytoplasm termed cytokinesis (Fig. 1). 

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. 

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. 

The vegetative cell cycle of S. cerevisiae has received extensive attention. There are many justifications for this. Firstly, the cell cycle in this organism has many convenient landmarks (Hartwell 1974, 1978 Pringle 1978) which make it very easy to identify the exact point in the cell cycle at which a cell happens to be. Examples of these landmark events include bud emergence, the size of the bud, mitosis (nuclear division takes place through the neck between the mother cell and the bud), and cell... 

Draetta, G., and Beach, D. (1988). Activation of cdc2 protein kinase during mitosis in human cells cell cycle-dependent phosphorylation and subunit rearrangement. Cell 54 17-24. 

Enoch, T and Nurse, P. (1990). Mutation of the fission yeast cell cycle control genes abolishes dependence of mitosis on DNA replication. Cell 60 665-673. 

Osmani, A. H., McGuire, S. L., and Osmani, S. A. (1991). Parallel activation of the NIMA and p34cdc2 cell cycle-regulated protein kinases is required to initiate mitosis in A. nidulans. EMBO J. 67 283-291. 

The Xenopus system has proven instrumental in determining the mechanism controlling exit from mitosis at the metaphase/anaphase transition. Studies in this area have relied heavily on extracts prepared from fully mature oocytes/ unfertilized eggs that are arrested at metaphase of the second meiotic division. Upon Ca2+ addition, anaphase is initiated and the extract enters the first embryonic cell cycle to replicate DNA. The activity responsible for metaphase arrest was discovered by Masui at the same time as MPF (Masui Markert 1971), and given the name cytostatic factor (CSF). CSF has never been purified... 

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... 

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