12609
Thrombopoietin ( TPO ), the primary physiological regulator of platelet production , was initially thought to be a lineage-specific factor acting predominantly on megakaryocytopoiesis .
 ( protein: TPO, None) , ( protein: Thrombopoietin, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( protein: TPO, None) , ( protein: Thrombopoietin, None) 