Mature Differentiated Cells, Stem Cells, Embryos, Cell division, Primary Culture, Nutrients, Malignant cells, Equilibrium

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	Mature Differentiated Cells All these cells in equilibrium may be shifted by manipulating the growth condition. The types of cells growing in culture are determined by their respective sources from where these have been derived, e.g. a huge number of stem cells are found in cell lines derived from embryos since they are capable of frequent cell division.
However, many of the cell lines grow for a limited number of subcultures (usually 8-10 subcultures, for a period of about 12 weeks). After this, they will either stop proliferating and die out, or will give rise to continuous cell lines that can be grown indefinitely Many normal cells do not give rise to continuous cell lines. For example, human fibroblast cells remain diploid for 50 generations after which they case to divide. But they are viable for up to another 18 months. The common features of continuous cell lines are: 1. Smaller, more rounded, less adherent cells with a higher nucleus-cytoplasmic ratio 2. Increased growth ratio. Time for cell doubling drops from 36-48 hrs to 12-36 hrs
3. Considerable variation among cells of a cell line due to aneuplodiy 4. Reduced dependence on serum 5. Increased cloning efficiency 6. Increased tendency to grow in suspension, decreased dependence on anchorage 7. Many cell lines become malignant, but some cell lines are normal and non-malignant 8. Growth is less dependent on cell density American Type Culture Collection (ATCC) maintains a large number of cell lines acquired from their originators. These cell lines are characterized before preservation and/or distribution on request to research workers. A cell line is multiplied and divided into a seed stock and a working or distribution stock
The seed stock is characterized and then maintained in state, preferably in liquid nitrogen at – 1960C. Seed stock are used to produce distribution stocks so that the cell line does change with time due to genetic instability, selection, senescence or transformation. Working stock or distribution stock consist of materials multiplied from the seed stock and used for further studies or for distribution