VEGFR-1 is associated with the proliferation of hematopoietic cells but not the number of BM HSCs. (A-B) The number of colony-forming units (CFU) in Vegfr-1 tk^–/– was decreased in all progenitor cells (BFU-E, CFU-GM, CFU-mixed) compared with that in wild-type mice (P = .013) (A). Each progenitor cell also showed a decrease in the number of colonies (P = .002 in BFU-E, .091 in CFU-GM, and .021 in CFU-mixed). Data represent the mean ± SEM for 3 mice. *P < .05; wild-type BM versus Vegfr-1 tk^–/– BM (B). (C) The number of HSCs (Sca-1⁺ and CD34⁺ cells) in BM was not influenced by Vegfr-1 tk deficiency. Percentages of HSCs among BMMNCs were analyzed by flow cytometer. Results represent the mean ± SEM for 3 mice.