Thrombin regulates S-phase re-entry by cultured newt myotubes

Curr Biol. 1999 Jul 29-Aug 12;9(15):792-9. doi: 10.1016/s0960-9822(99)80362-5.


Background: Adult urodele amphibians such as the newt have remarkable regenerative ability, and a critical aspect of this is the ability of differentiated cells to re-enter the cell cycle and lose their differentiated characteristics. Unlike mammalian myotubes, cultured newt myotubes are able to enter and traverse S phase, following serum stimulation, by a pathway leading to phosphorylation of the retinoblastoma protein. The extracellular regulation of this pathway is unknown.

Results: Like their mammalian counterparts, newt myotubes were refractory to mitogenic growth factors such as the platelet-derived growth factor (PDGF), which act on their mononucleate precursor cells. Cultured newt myotubes were activated to enter S phase by purified thrombin in the presence of subthreshold amounts of serum. The activation proceeded by an indirect mechanism in which thrombin cleaved components in serum to generate a ligand that acted directly on the myotubes. The ligand was identified as a second activity present in preparations of crude thrombin and that was active after removal of all thrombin activity. It induced newt myotubes to enter S phase in serum-free medium, and it acted on myotubes but not on the mononucleate precursor cells. Cultured mouse myotubes were refractory to this indirect mechanism of S-phase re-entry.

Conclusions: These results provide a link between reversal of differentiation and the acute events of wound healing. The urodele myotube responds to a ligand generated downstream of thrombin activation and re-enters the cell cycle. Although this ligand can be generated in mammalian sera, the mammalian myotube is unresponsive. These results provide a model at the cellular level for the difference in regenerative ability between urodeles and mammals.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Differentiation / drug effects
  • Cells, Cultured
  • Culture Media
  • Extremities
  • Mice
  • Muscle, Skeletal / cytology
  • Regeneration
  • S Phase / drug effects*
  • S Phase / physiology
  • Salamandridae / anatomy & histology
  • Salamandridae / physiology*
  • Species Specificity
  • Thrombin / pharmacology*


  • Culture Media
  • Thrombin