FIP200 is cell-autonomously required for the maintenance of fetal HSCs. (A) Diagram of the competitive repopulation experimental design for data in panels B-C. Fetal liver cells (200 000) from CD45.2⁺ FIP200^F/F;Mx1-Cre or control mice were injected into lethally irradiated CD45.1⁺ wild-type recipients along with 500 000 CD45.1 bone marrow cells. Five pIpC injections were administered to one set of recipients every other day beginning 5 days after transplantation. Reconstitution of peripheral blood by donor cells was then monitored for additional 16 weeks (at the 4th, 6th, 10th, and 18th weeks after transplantation). No pIpC was administered to the other set of recipients. Reconstitution of peripheral blood by donor cells was examined at the 4th week after transplantation. The dashed vertical lines indicate the time points to monitor the donor contribution. (B) Contribution of fetal liver-derived CD45.2-expression (donor) cells to peripheral blood leukocytes in reconstituted mice in the group with pIpC treatment. Shaded bar in panel B indicates the pIpC administration. (C) Contribution of donor cells to peripheral blood lineages, including myeloid (Mac1⁺, Gr1⁺), B-cell (B220⁺), and T-cell (CD3⁺) lineages in the group with pIpC treatment. (D) Contribution of donor cells to peripheral blood leucocytes in reconstituted mice in the group without pIpC treatment. Data represent the average donor chimerism levels from 3 independent experiments with a total of 9 recipients per genotype.