(A) Myeloid progenitor cell colony formation of fetal liver cells (6 × 10⁴) from control and Brpf1^fl/fl Vav1-iCre (vKO) embryos at E15.5. Colonies were examined at day 9, and average numbers of burst-forming unit-erythroid (BFU-E), colony-forming unit-granulocyte/monocyte (CFU-GM), and colony-forming unit-granulocyte/erythrocyte/monocyte/megakaryocyte (CFU-GEMM) colonies are presented. n = 4 for each group. (B) Morphology of representative individual colonies formed from control and vKO fetal liver cells. Images were obtained with an AxioCam HRc digital camera and a 20× objective on an AXIO Zoom.V16 microscope. Scale bar: 1 mm. (C) Survival curves of irradiated C57BL/6 mice without transplantation (dashed line) or transplanted with 2 × 10⁵ control (solid black line) or vKO (solid red line) fetal liver cells at E14.5. n = 13 for the group without transplantation and n = 9 for each transplanted group. (D) CFU-S analysis at day 12. Images of spleens are shown on the left and the colony numbers are presented in the graph on the right. n = 5 for each group. Scale bar: 5 mm. (E and F) Brpf1 inactivation impairs long-term hematopoietic reconstitution potential in the fetal liver. Fetal liver cells were collected for tail-vein injection into irradiated C57BL/6.SJL mice. Flow cytometric analysis of the contribution of donor (CD45.2⁺) cells and multilineage engraftment in the recipients’ peripheral blood at 4 to 16 weeks after transplantation is shown in E, whereas fractions of donor-derived cells in specific cell populations in the recipients’ bone marrow at 22 weeks are presented in F. E12.5 and E15.5 mutant fetal liver cells showed similar defects in hematopoietic reconstitution, and the data are from 6 pairs of wild-type and mutant embryos (3 pairs at E12.5 and 3 pairs at E15.5). **P < 0.01, ***P < 0.001. For A, D (right), E, and F, unpaired 2-tailed Student’s t tests were performed and average values are shown as the mean + SEM.