Reversibility of the megakaryoblastic proliferative disorder. (A-D) C57BL/6 and GATA-1Lo (G1Lo) mice received daily intraperitoneal injection of flavopiridol (7 mg/kg per day) for 7 consecutive days, followed by 2 weeks of no treatment. (A,B) Platelet counts and hematocrits were obtained on days 0, 7, and 21 as indicated. Each line represents an individual mouse. (A,B) Two independent experimental trials. (C) Representative mice were killed at days 0, 7, and 21. Sections from femurs were stained with hematoxylin and eosin (original magnification ×400). Arrows show examples of cells with blastic morphology. (D) Flow cytometry on marrows from mice in panel C.