Size and hematopoietic characteristics of raf-1^-/- mice. (A) The weight (gm) for raf-1^+/+ (n = 18) and raf-1^-/- (n = 16) littermates at 18 to 21 days after birth is presented as the mean ± SD. The size difference is readily appreciated beginning 2 to 3 days after birth. (B) Circulating platelet counts for raf-1^+/+ (n = 21) and raf-1^-/- (n = 15) littermates at 18 days after birth are presented, with the mean value indicated by the bar. The mean (± SD) values (× 10³) are 832 ± 102 (raf-1^+/+) and 929 ± 94 (raf-1^-/-); P = .006. (C) The mean percentage (± SD) of CD41⁺ cells in freshly harvested bone marrow from raf-1^+/+ (0.12%) and raf-1^-/- (0.17%) littermates are presented; n = 3 for each genotype. Student t test analysis indicates that the 2 groups are not statistically different; P = .12. (D) The relative representation of colony-forming progenitor cells per 50 000 low-density bone marrow mononuclear cells from raf-1^+/+ (n = 9) and raf-1^-/- (n = 6) littermates at 18 days after birth is presented. Colonies were generated in methylcellulose media supplemented with SCF, IL-6, IL-3, EPO, and TPO. CFU-GM indicates colony-forming unit granulocyte-macrophage; BFU-E, blast-forming unit erythrocyte; CFU-Mix, 3 lineages or less; and CFU-MK, CFU megakaryocyte. Error bars indicate means ± SD.