Spred2 is downstream of FoxO3a and mediates granulopoiesis. (A) Spred2 but not SOCS3 expression in Lin⁻Sca1⁺c-Kit⁺ (LSK) cells was down-regulated in FoxO3a-deficient mice. Data are means plus or minus SD of Spred2 or SOCS3 expression relative to GAPDH in FoxO3a-deficient LSK cells (■; n = 5) relative to wild-type LSK (□; n = 5) cells. *P < .01. (B) Spred2-deficient mice develop granulopoiesis during hematopoietic recovery following 5-FU injection. Data shown are means plus or minus SD of WBCs (×1000/μL), platelets (×10⁴/μL), or Hb (g/dL) of Spred2-deficient (■; n = 5) or wild-type (□; n = 5) mice. (C,D) AKT and ERK are activated in HSCs of FoxO3a-deficient mice during hematopoietic recovery after 5-FU–induced myelosuppressive stress. BM mononuclear cells (unfractionated) or Lin⁻Sca-1⁺ cells were isolated from 8- to 12-week-old Spred2-deficient or wild-type mice 2 days after 5-FU injection and stained with phospho-AKT (C) or phospho-ERK (D), and the frequency of phospho-AKT (C)– or phospho-ERK (D)–positive cells was determined. Data are mean frequency (%) plus or minus SD of phospho-AKT or ERK-positive cells. *P < .05.