Consideration of the Role of the Cell Cycle in Growth Factor Modulated Responses
The interval between consecutive mitoses has been termed the cell cycle and during this interval the cell must increase cellular mass by duplicating cellular components, replicate its DNA, and undergoing an orderly division to equal progeny cells (Baserga, 1984, 1985). The modulation of G1 events by growth factors provide much of the regulation for cellular proliferation. Normal cells become growth-arrested in vitro when they reach confluent density in culture conditions; cells may also be arrested at subconfluent densities by depriving them of serum growth factors. These quiescent cells are reversibly growth arrested in the G0 phase. When G0-arrested fibroblasts are stimulated to re-enter the cell cycle by the addition of fresh serum, there is a characteristic lag before the onset of DNA synthesis. This lag describes the G1 phase of the cell cycle. A fibroblastic culture system provides a unique way to investigate the growth factor regulation of G1-specific events.
KeywordsPDGF Receptor Growth Factor Regulation Serum Growth Factor Competence Formation Confluent Density
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