Cycling HSCs are sensitive to the loss of Phf6. (A) Strategy for competitive repopulating assays using the Mx1-Cre system. Mx1-Cre;Phf6^wt/y and Mx1-Cre;Phf6^fl/y mice were injected with pIpC at 2 or 9 weeks of age and BM cells were harvested for competitive transplantation at 5 or 12 weeks of age, respectively. CD45.2 BM cells (5 × 10⁶) were transplanted into lethally irradiated CD45.1 recipient mice along with the same number of CD45.1 WT BM cells. (B) The chimerism of CD45.2 donor cells in PB after transplantation (n = 5 or 6). (C) The chimerism of My, B-, and T-cell lineages in PB and those of HSCs and progenitors 16 weeks after transplantation are shown (n = 5 or 6). Data are shown as the mean plus or minus SEM. *P < .05, **P < .01, ***P < .001 by the Student t test.