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Erythropoietin ( Epo ), the primary regulator of the production of erythroid cells , acts by binding to a cell surface receptor ( EpoR ) on erythroid progenitors .
 ( protein: Epo, None) , ( cell type: erythroid progenitors, None) , ( protein: cell surface receptor, None) , ( cell type: erythroid cells, None) , ( protein: EpoR, None) , ( protein: Erythropoietin, 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: Epo, None) , ( cell type: erythroid progenitors, None) , ( protein: cell surface receptor, None) , ( cell type: erythroid cells, None) , ( protein: EpoR, None) , ( protein: Erythropoietin, None) 