Cell division factors

N,N -Diphenylurea is a compound isolated and identified as a cell-division factor of coconut milk which exerts the same activity as the N6-substituted adenines in the cytokinin tests 45). Bruce and Zwar synthesized a number of ring substituted derivatives and determined their activity46. We tried to analyze quantitatively their data for derivatives where one of the benzene rings is unsubstituted (22)44). 

Zeatin (frans-iV -[4-hydroxy-3-methylbut-2-en-l-yI]adenine) [1637-39-4] M 219.3, m 207-208, 209-209.5 , pKi 4.4 (basic), pK2 9.8 (acidic). Purified by recrystn from EtOH or H2O. The UV has A-max at 207 and 275nm (e 1400 and 14650) in O.IN aqueous HCl 212 and 270nm (e 17050 and 16150) in aqueous buffer pH 7.2 220 and 276nm (e 15900 and 14650) in O.IN aq NaOH. Thepicrate has m 192-194 (from H2O) from which zeatin can be recovered by treatment with Dowex 1 x8 (200-400 mesh, OH form). [Letham et al. Aust J Chem 22 205 1969 Proc Chem Soc (London) 230 7964 Shaw and Wilson Proc Chem Soc (London) 231 7964.] It is a cell division factor (plant growth regulator) [Letham and Palni Ann Rev Plant Physiol 34 163 1983] and inhibits mitochondrial function [Miller Plant Physiol 69 1274 7982]. Its 9-riboside is a cytokine [McDonald and Morris Methods Enzymol 100 347 7985]. 

C10H9N5O, Mr 215.21, mp. 267°C. K. belongs to the cytokinin group and is a derivative of adenine it occurs in various higher plants and yeasts and acts as a cell division factor. Like the closely related zeatin, K. is still active at million-fold dilutions and is thus considered to be a plant hormone. K. is isolated from autoclaved, aqueous slurries of deoxyribonucleic acids and is sometimes considered to be an artefact. K. is used as a plant growth regulator and also for inducing callus formation in plant cell cultures, etc.. ... 

However it is becoming increasingly difficult to assign naturally-occurring hydroxamic acids unequivocally to such classes as antibiotics, growth factors, tumor inhibitors, cell division factors, pigments and siderophores as the distinctions between there activity classes are becoming less clear. 

S. Increased synthesis of transforming growth factor-beta , which blocks cell division and promote.s apoptosis by interacting with its own membrane recepror,... 

ITowever, most normal somatic cells lack telomerase. Consequently, upon every cycle of cell division when the cell replicates its DNA, about 50-nucleotide portions are lost from the end of each telomere. Thus, over time, the telomeres of somatic cells in animals become shorter and shorter, eventually leading to chromosome instability and cell death. This phenomenon has led some scientists to espouse a telomere theory of aging that implicates telomere shortening as the principal factor in cell, tissue, and even organism aging. Interestingly, cancer cells appear immortal because they continue to reproduce indefinitely. A survey of 20 different tumor types by Geron Corporation of Menlo Park, California, revealed that all contained telomerase activity. 

All mature blood cells arise from primitive hematopoietic cells in the bone marrow, the pluripotent stem cells. Approximately 0.1% of the nucleated cells of the bone marrow are pluripotent stem cells and approximately 5% of these cells may be actively cycling at any one time. The stem cell pool maintains itself through a process of asymmetrical cell division when a stem cell divides, one daughter cell remains a stem cell and the other becomes a committed colony-forming cell (CFC). The proliferation and differentiation of CFCs are controlled by hematopoietic growth factors. The hematopoietic growth factors stimulate cell division, differentiation and maturation, and convert the dividing cells into a population of terminally differentiated functional cells. 

Nurse I wonder whether the word timer is perhaps the most useful one. You probably came up with the term timer to contrast it with counting cell divisions. It is a timer that is influenced enormously by external factors, and in vivo it will be... 

Simon I don t think it is known. Some years ago researchers rounded up the usual suspects from yeast, complemented yeast mutants and checked for the expression patterns of factors such as the cyclins and Cdcs in plant meristems. They saw some spotty expression patterns in the meristems, but there were no clear domains of down-regulation of cell divisions, for example. 

Simon Yes, because there is no cell migration. If you want to construct a lobed leaf, for example, you have to define areas where cell divisions are still going on while in the adjacent areas they have stopped. We don t know how this is done. Apoptosis is a factor that is only occurring in a very few cases in plant development. It is controlled division that is important. 

De Benedetti, A., Joshi-Barve, S., Rinker-Schaeffer, C., and Rhoads, R. E. (1991). Expression of antisense RNA against initiation factor eIF-4E mRNA in HeLa cells results in lengthened cell division times, diminished translation rates, and reduced levels of both eIF-4E and the p220 component of eIF-4F. Mol. Cell Biol. 11, 5435-5445. 

Some growth factors may be classified as cytokines (e.g. interleukins, TGF-P and CSFs). Others (e.g. IGFs) are not members of this family. Each growth factor has a mitogenic (promotes cell division) effect on a characteristic range of cells. Whereas some such factors affect only a few cell types, most stimulate growth of a wide range of cells. 

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