A role for GATA-3 in the maintenance of hematopoiesis. (A) Chimerism was analyzed in primary recipient mice 16-20 weeks after injection of a 1:1 ratio of fetal liver cells from Gata3^z/z (CD45.2) or littermate control Gata3^+/+ (CD45.2) and adult BM cells (CD45.1). Donor-derived absolute cell numbers (top) per mouse (2 femurs plus 2 tibias) and cell ratios (bottom) in BM LSK (left panels) and LSK CD150⁺CD48⁻CD34⁻ (right panels) populations were determined by flow cytometry. Recipient mice were considered to be engrafted when > 1% CD45.2⁺CD45.1⁻ myeloid cells were of the donor immunophenotype. Data represent the summary of 4 independent experiments and 6 recipient mice in each group with SEM. *P < .003; #P < .03. NS indicates not significant. (B) Mature lineage cells in peripheral blood were analyzed by flow cytometry every 4 weeks for 16 weeks after transplantation for lineage-specific markers and CD45. The contribution of fetal liver donor-derived cells (CD45.2⁺CD45.1⁻) to myeloid (Gr1⁺ Mac1⁺), B-lymphoid (CD19⁺), and T-lymphoid (Thy1.2⁺CD3⁺) lineages from Gata3^+/+ (+/+, ●) or Gata3^z/z (z/z, ▵) cells are shown. Data represent the summary of 5 independent experiments and an average of 12 recipient mice in each group with SEM. *P < .001. (C) The frequency of long-term repopulating cells was determined in vivo by administering different doses of donor LSK cells. The indicated number (horizontal axis) of Gata3^+/+ (+/+, ●) or Gata3^z/z (z/z, ▵) LSK CD45.2⁺CD45.1⁻ cells from primary recipients were transplanted into lethally irradiated secondary recipients along with 2 × 10⁵ CD45.1 adult BM cells. Recipient mice that were engrafted by more than 1% with CD45.2⁺CD45.1⁻ myeloid and B cells in peripheral blood for 16 weeks after transplantation were scored as positive and were used to calculate the HSC frequency in the primary recipients (also see supplemental Table 1).