Effect of aging and transplantation on the differentiation potential of CRUs. Mice that had been repopulated with a single, fresh (□) or homed (▨) CRU were identified as described in the Figure 4 legend and in “Materials and methods.” The lineage composition of clones generated by single, young, or old HSCs in old or young hosts was defined as the proportion of donor (Ly-5.2⁺)-derived leukocytes expressing markers for B (CD45R/B220⁺) or T (CD90/Thy-1.2⁺) lymphocytes or for myeloid (Gr-1/Ly6G⁺ and Mac-1/CD11b⁺) cells. Values shown for the 3 combinations of variably aged donors and recipients represent the mean ± SEM of 2 pooled experiments with 3 to 6 mice per group. Note that data for the young-to-young group were collected contemporaneously with those for other groups but were, in part, reported in Szilvassy et al.²³