BM content of HSPCs is reduced in number in Mll^PTD/WTmice. (A) BM of age- and sex-matched littermate WT controls and Mll^PTD/WT mice were analyzed at 2, 4, and 12 months of age, based on the immunophenotype analysis. Representative flow cytometry (FACS) contour diagram shows the frequency of LSK and LSK/SLAM⁺ BM cells of WT and Mll^PTD/WT mice. Shown is a representative of 8 experiments with similar results. (B) Absolute number of LSK cells of WT and Mll^PTD/WT mice. Mll^PTD/WT LSK population is reduced in absolute number during aging (n = 8). The difference between control and Mll^PTD/WT was significant at 8 and 12 months. *P < .05. (C) Absolute number of LSK/SLAM⁺ cells of WT and Mll^PTD/WT mice. Mll^PTD/WT LSK/SLAM⁺ populations are reduced in absolute number during aging (n = 8). The difference between control and Mll^PTD/WT was significant at 4, 8, and 12 months. *P < .05. **P < .01. (D) Absolute number of progenitors HPC, GMP, common myeloid progenitor cells (Lin⁻c-Kit⁺Sca1⁻CD34⁺CD16/32^mid; CMPs), and MEP of WT and Mll^PTD/WT mice. Mll^PTD/WT mice GMP population is increased at the expense of the MEP population (2 experiments, n = 8; 4-month-old mice were used). The differences of GMP and MEP between control and Mll^PTD/WT were significant (P < .05). (E) Apoptosis was checked by annexin V staining. Data are the mean percentage ± SD of annexin V⁺/7 AAD⁻ and annexin V⁺/7 AAD⁺. *P < .05. **P < .01. Experiments were performed in duplicate groups for 4 mice at 4-month-old per genotype repeated in 3 separate experiments. (F) Cell-cycle analysis was performed with a BrdU flow kit. Percentage of cycling cells: G₀/G₁ and S/G₂/M are shown for LK (Lin⁻Kit⁺) and LSK fractions (2 experiments, n = 4; 4-month-old mice were used). *P < .05. (G) H3K4 methylation in LSK fractions. BM cells were harvested and LSK cells were selected using autoMACS. Western blots were done using indicated antibodies (anti-H3K4me3, anti-H3K4me2, and anti-H3). Representative data were from 3 independent experiments.