Fig 1: The Phenotypic HSC Compartment Changes with Age(A) Representative flow cytometric data of young and aged bone marrow (BM): MPP, multipotent progenitor; LMPP, lymphoid-primed multipotent progenitor; Fr 1, fraction 1; Fr 2, fraction 2; Fr 3, fraction 3.(B) Frequency of the HSC/MPP population (left) and HSC subpopulations (right) in young and aged BM (as detailed in A). Dots represent individual mice, and horizontal lines indicate median ± SD.(C) Summary of primary and secondary transplantation experiments to test potential of young and aged single phenotypic HSCs. Single CD34-KSL, fraction 1, fraction 2, or fraction 3 cells were sorted from BM cells of Kusabira Orange (KuO) mice and were individually transplanted with 2 × 105 BM competitor cells from Ly5.1/Ly5.2-F1 mice into lethally irradiated Ly5.2 mice. Chimerism of KuO+ neutrophils/monocytes, erythrocytes, platelets, B cells, and T cells in peripheral blood (PB) was analyzed at 2, 3, 4, 8, (12), 16, (20), and 24 weeks after primary transplantation. Secondary transplantation assays were performed by transferring 1 × 107 whole BM cells from primary recipient mice. PB chimerism was analyzed 4, 12, 16, 20, (and 21–22) weeks in secondary recipients.(D) PB chimerism of individual single young and aged HSCs in a total of 421 primary recipients (as described in C), separated based on lineage output.(E) Estimated frequency of functional HSCs, CMRPs, MERPs, MkRPs, and “other” within the young and aged pHSC compartment, derived from single-cell transplantation assays (Table 1). CMRPs, MERPs, and MkRPs are subsets of MyRPs. “Non-reconstituting” denotes no PB reconstitution of KuO+ cells in primary recipients.