PROLIFERATION
Proliferation, i.e. repetitive cell divisions, allows to form a multicellular organism from a single cell (zygote).
2. PROLIFERATION CONTROL
This cellular division is strictly controlled by growth factors (GFs), growth inhibitors and other controlling molecules. Growth factors can act on cells in different phases of the cell cycle. Each cell responds to specific combinations of signalling molecules incl. GFs; different cells can respond differently to the same signal (e.g. growth factor). Examples of GFs are shown in the Table; at least two examples are required in final examination.
| Growth factor | Cells proliferating in response to GF | |
| EGF NGF PDGF FGF IGF-1 IL-2 EPO VEGF HGF |
epidermal GF nerve GF platelet-derived GF fibroblast GF insulin-like GF 1 interleukin-2 erythropoietin vascular endothelial GF hepatocyte GF |
keratinocytes, trophoblast, neuroepithelial cells etc. neuroblasts, neurite growth connective tissue cells, neuroglia many cell types acts with other GFs activovated T lymphocytes precursors of erythrocytes endothelial cells hepatocytes |
Growth factors can influence only those cells that possess specific receptors for the particular growth factor. The receptors for most growth factors are transmembrane Tyrosine-specific protein kinases. Through their activation, growth factors trigger cascades of intracellular signals and activate new genes. Some growth factors can also act as differentiation factors.
Although the proliferation is responsible for the growth of the embryo, there are many more mechanisms contributing to the growth of the body:
• proliferation – hyperplastic growth,
• enlargement of cell size – hypertrophic growth,
• production and accumulation of the extracellular matrix.
More pieces of information concerning “The Cell Cycle” can be found in the electronic course “Cytology II”.