Epo-induced erythroid maturation is dependent on Plcγ1 signaling

Erythropoiesis is a tightly regulated process. Development of red blood cells occurs through differentiation of hematopoietic stem cells (HSCs) into more committed progenitors and finally into erythrocytes. Binding of erythropoietin (Epo) to its receptor (EpoR) is required for erythropoiesis as it promotes survival and late maturation of erythroid progenitors. In vivo and in vitro studies have highlighted the requirement of EpoR signaling through Janus kinase 2 (Jak2) tyrosine kinase and Stat5a/b as a central pathway. Here, we demonstrate that phospholipase C gamma 1 (Plc gamma 1) is activated downstream of EpoR-Jak2 independently of Stat5. Plc gamma 1-deficient pro-erythroblasts and erythroid progenitors exhibited strong impairment in differentiation and colony-forming potential. In vivo, suppression of Plc gamma 1 in immunophenotypically defined HSCs (Lin(-)Sca1(+)KIT(+)CD48(-)CD150(+)) severely reduced erythroid development. To identify Plc gamma 1 effector molecules involved in regulation of erythroid differentiation, we assessed changes occurring at the global transcriptional and DNA methylation level after inactivation of Plc gamma 1. The top common downstream effector was H2afy2, which encodes for the histone variant macroH2A2 (mH2A2). Inactivation of mH2A2 expression recapitulated the effects of Plc gamma 1 depletion on erythroid maturation. Taken together, our findings identify Plc gamma 1 and its downstream target mH2A2, as a 'non-canonical' Epo signaling pathway essential for erythroid differentiation.