51-55

Cell Division and Growth Factors

• Connective Tissue Cell Culture

  • A sample of human connective tissue is cut into small pieces.
  • Cells anchor to the surface of the Petri dish and begin to divide, demonstrating anchorage dependence.
  • Cells stop dividing when they form a complete single layer, indicating density-dependent inhibition.

• Extracellular Matrix and Fibroblast Culture

  • Enzymes are used to digest the extracellular matrix in the tissue pieces, resulting in a suspension of free fibroblasts.
  • Cells are transferred to culture vessels with a basic growth medium, which consists of:
  • Glucose
  • Amino acids
  • Salts
  • Antibiotics (to prevent bacterial growth)
  • Platelet-Derived Growth Factor (PDGF) is added to half of the vessels.
  • Cultures are incubated at 37°C for 24 hours.

• Control Experiment Without PDGF

  • In the control medium without PDGF, fibroblast cells do not divide.

• Experiment With PDGF

  • In the medium with PDGF, fibroblast cells proliferate.
  • Scanning Electron Microscopy (SEM) shows cultured fibroblasts.

• Cell Density and Division Gaps

  • If some cells are scraped away, the remaining cells divide to fill the gap, stopping once they are in contact with one another (density-dependent inhibition).
  • Normal mammalian cells need contact with neighboring cells, nutrients, growth factors, and a substratum for attachment to limit cell density to a single layer.

• Role of PDGF

  • PDGF signals cells by binding to a cell-surface receptor, which then becomes phosphorylated, activating it to transduce a signal.
  • Researchers inquire about the effects of adding a chemical that blocks phosphorylation on these results.
  • PDGF is produced by blood cell fragments (platelets).
  • PDGF stimulates division of cultured fibroblasts in artificial conditions as well as