Figure 2.

p53 Deficiency Leads to Proliferative Exhaustion of Fanca^−/− HSCs

(A) p53 deficiency decreases Fanca^−/− HSC quiescence. BM cells from mice with the indicated genotype at 8 and 20 weeks of age were gated for CD34⁻ LSK population and analyzed for BrdU incorporation. Representative plots for 20 weeks (left) and quantification for both 8 and 20 weeks (right) are shown. Results are means ± SD of two independent experiments (n = 6 per group).

(B) Loss of p53 promotes Fanca^−/− HSPC proliferation. LSK cells isolated from mice with the indicated genotype at 8 and 20 weeks of age were plated in cytokine-supplemented methylcellulose medium. Colonies were enumerated on day 7 after plating. Results are means ± SD of three independent experiments (n = 9 per group).

(C) Loss of p53 causes progressive decline in repopulating potential of Fanca^−/− HSCs. 50 SLAM cells from mice with the indicated genotype (CD45.2) at 20 weeks of age, along with 4 × 10⁵ protector BM cells (CD45.1), were transplanted into lethally irradiated Boy J recipients. Donor-derived chimera was detected by flow cytometry at the indicated weeks post-transplant.

(D) Competitive repopulating units (CRUs) determined by limiting dilution BM transplantation assay. Graded numbers of test SLAM cells (CD45.2+) from mice with the indicated genotype at 20 weeks of age were mixed with 4 × 10⁵ protector BM cells (CD45.1) and transplanted into irradiated congenic recipients (CD45.1⁺). Plotted are the percentages of recipient mice containing less than 1% CD45.2⁺ blood nucleated cells at 16 weeks after transplantation. The frequency of functional HSCs was calculated according to Poisson statistics.

^∗p < 0.05; ^∗∗p < 0.01.