Rac excision in Nestin⁺ cells is associated with decreased HSCs and progenitors. Immunophenotypically-defined HSC (Lineage^–/lowSca-1⁺ckit⁺), respectively, HSC-1 (Lineage^–/lowSca-1⁺ckit⁺CD150^+/highCD48^–), HSC-2 (Lineage^–/lowSca-1⁺ckit⁺CD150^+/lowCD48^–) in (A) BM. (B) Schematic representation of competitive repopulation assay. (C) 1 000 000 of BM Lineage^– cells from TG Rac1^Δ/Δ Rac3^−/− (CD45.2) were injected into lethally-irradiated recipients (CD45.1/CD45.2) along with 500 000 BM Lineage^– competitor cells (CD45.1). Percentages of donor-derived chimerism in peripheral blood (PB) are shown at 4, 8, and 12 weeks posttransplant. Data represent mean ± SD of the percentages of donor-derived cells in the PB of recipients after infusion from 1 experiment with 4 recipients for each population, ***P < .0001. (D) Immunophenotypically defined (as in [A]) HSCs in spleen. All values are mean ± SEM, *P < .05, ** P < .01, N = 6 mice from 3 independent experiments; ns, not significant. Comparison of mRNA levels of HSCs maintenance genes, (E) stem cells factor (Scf) total, (F) m220 Scf (membrane-bound isoform), and (G) Cxcl12 from freshly sorted Nestin⁺ cells from TG WT and TGRac1^Δ/Δ/Rac3^−/− mice by quantitative real-time PCR. Data represent mean ± SEM, N = 3, *P < .05.