library_construction_protocol: In brief, intact bone marrows from mice at the age of 2-4 months or 18-24 months were flushed from mouse femora and tibiae. Bone marrow cells by pipetting with 1 mL syringe, and then underwent red blood cell lysis using 0.16 M ammonium chloride solution. Genomic DNA extraction, library preparation, and sequencing were performed by using the Hyperactive Universal CUT&Tag Assay Kit for Illumina Pro (TD904, Vazyme). 5×104 sorted HSCs were collected at room temperature and incubated overnight with canavalin A beads and Acetyl-Histone H3K9ac antibody (9649, CST) at 4 ℃. Genomic DNA was fragmented using pA/pG-Tn5 transposons and extracted using DNA Extract Beads. Using DNA as a template for PCR, sequencing libraries were generated by adding Illumina sequencing adapters with custom primers. The resulting library DNA was purified using VAHTS DNA Clean Beads (N411, Vazyme).