Cluttered environment for TPO

Separate reports in Nature detail the cloning and biological testing of thrombopoietin (TPO), the cytokine believed to be responsible for platelet replenishment. The discovery ends a 30-year search for the factor, which proved to be far more difficult to isolate than other blood cell growth factors such as erythropoietin, G-CSF and GM-CSF.

ZymoGenetics Corp. cloned and sequenced the mouse version of TPO, and showed that the recombinant protein stimulated platelet production after injection into mice. Levels of platelets increased fourfold, a week after the injection.