New cell cycle

Li WX, Cui CB, Cai B, Yao XS. Labdane-type diterpenes as new cell cycle inhibitors and apoptosis inducers from Vitex trifolia L. J Asian Nat Prod Res 2005 7 95-105. 

When mitosis has been completed, the cell requires signals in the form of growth factors to direct towards a new roimd of division. The signals become effective in the first two-thirds of Gi phase. In this time window, the cell is programmed to begin a new cell cycle or to enter Go phase. After a particular point, the restriction point R, no further signals are needed to continue the cell cycle. The cell cycle apparatus is self-contained from this point onwards. S, G2 and M phase occur without external control. The cell cycle may still be halted after crossing the restriction point, however, if the cell detects, via internal control mechanisms or checkpoints, that defects have occurred in the correct course of the phases. 

We wish to surest that the primary factor of this unified control is the constitution of a single nucleus, and that the enclosure of the two parental genomes within a single nuclear membrane results in the establishment of a new basic rate of DNA synthesis and chromosome replication which defines the new cell cycle to which all subsequent activities of the parental genomes are thereafter adjusted. 

Returning to the reverse process, i.e., to cell fusion, the conclusion appears to us justified that the formation of a single nucleus is the essential condition for, or the direct cause of, the establishment of a single new cell cycle in hybrid cells. 

If these assumptions are accepted, the initial hypothesis may be restated more completely as follows In interspecific hybrids, the replication and configurational changes of all chromosomes, as well as the transcription of the homologous genes governing the different syntheses tvhich result in cell doubling, are timed with reference to a single fixed point of the new cell cycle. 

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. 

Hasinoff, B. B. Wu, X. Yalowich, J. C. Goodfellow, V. Laufer, R. S. Adedayo, O. Dmitrienko, G. I. Kinamycins A and C, bacterial metabolites that contain an unusual diazo group, as potential new anticancer agents antiproliferative and cell cycle effects. Anti-Cancer Drugs 2006, 17, 825-837. 

Clarke, P. R., and Karsenti, K. (1991). Regulation of p34cprotein kinase new insights into protein phosphorylation and the cell cycle. J. Cell Sci. 100 409-414. 

Mailer Murakami and Vande Woude published a nice paper a couple of years ago where they took a Mos arrest ed blastomere and re-started the cell cycle with Ca2+, getting a new cycle of tyrosine phosphorylation equivalent to cycle one, even though the embryo was actually entering cycle two or three. This would suggest that MAP kinase sets the timer back to zero. Of course, MAP kinase is very high in the unfertilized egg, the cell in which the timer is activated. 

Nasmyth The question is, will their regulation be any different from that of things that aren t cell cycle regulators At the end of the day the String promoter is the promoter of a cell cycle gene, but would you learn anything new about transcription ... 

Endo, T. and Nidal-Ginard, B. (1988) SV40 large T antigen induces reentry of terminally differentiated myotubes into the cell cycle. In Kedes, L.H. and Stockdale, F.E. (eds) Cellular and Molecular Biology of Muscle Development. Alan R. Liss, New York, pp. 95-104. 

Frahm SO, Rudolph P, Dworeck C, et al. Immunoenzymatic detection of the new proliferation associated protein plOO by means of a cellular ELISA specific detection of cells in cell cycle phases S, G2 and M. J. Immunol. Methods 1999 223 147-153. 

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