Yy1 does not synergize with PRC2 and has a role enhancing HSC/progenitor activity. (A) Peripheral blood platelet (top panel) and white blood cell counts (bottom panel) at 7 weeks of age from Mpl^−/− mice of the given genotypes. The horizontal bar shows the mean for n = 11 to 40 samples. (B) Fetal liver cellularity (left), proportion (middle), and number (right) of LSK cells per E14.5 fetal liver of the given genotype. Data are from one litter of 4 Yy1^+/+ and 5 Yy1^+/− embryos, representative of data from 3 independent litters. (C) Fetal liver LSK cells from 4 to 5 individual CD45^Ly5.2 donor embryos of the given genotype were mixed with an equal number of wild-type CD45^Ly5.1 competitor fetal liver LSK cells (n = 2 samples) and used to reconstitute 4 lethally irradiated recipients per donor sample. Contribution of test cells to each hematopoietic organ and LSK cells is shown for 12 to 16 weeks after reconstitution. Blood indicates peripheral white blood cells. (D) E14.5 fetal liver cells were infected with retrovirus carrying shRNAs against Yy1 or a nonsilencing control (Nonsil) and used to reconstitute lethally irradiated recipients. The proportion of cells infected with each shRNA (GFP⁺) was compared at input and at 6 to 12 months after reconstitution in spleen, thymus, bone marrow, and the LSK cell compartment. The effect of the Nonsil shRNA in each of 3 experiments was normalized to 1. Statistical significance *P < .05, **P < .01, ***P < .001, corrected for multiple testing; error bars indicate SEM.