Histopathologic analysis. (A) Representative peripheral blood smears (×1000 magnification) from control, Ezh2^−/−, Jak2^VF/+, and Jak2^VF/+ Ezh2^−/− mice at 24 weeks after pI-pC injection are depicted. The Jak2^VF/+ Ezh2^−/− blood film shows leukoerythroblastic anemia, with predominance of nucleated RBC and neutrophils; a rare blast is shown in the inset. (B) Hematoxylin and eosin staining of representative BM sections (×500 magnification) from control, Ezh2^−/−, Jak2^VF/+, and Jak2^VF/+ Ezh2^−/− mice at 24 weeks after pI-pC injection is shown. (C-D) Hematoxylin and eosin–stained spleen sections from control, Ezh2^−/−, Jak2^VF/+, and Jak2^VF/+ Ezh2^−/− mice at lower (×40) and higher (×500) magnifications are presented. (E-F) Reticulin staining on representative (E) BM and (F) spleen sections (×500 magnification) from control, Ezh2^−/−, Jak2^VF/+, and Jak2^VF/+ Ezh2^−/− mice at 24 weeks after pI-pC injection are shown. Note that concomitant deletion of Ezh2 in Jak2V617F mice results in extensive fibrosis in the BM and spleens, with leukoerythroblastic anemia and thrombocytosis in the blood.