Figure 4. CXCL12 produced by osteoblasts promotes the maintenance of early lymphoid progenitors but not HSCs.

a, b, Cellularity (a, n=4) and HSC frequency (b, n=4) in the bone marrow and spleen of Col2.3-cre; Cxcl12^fl/fl mice and littermate controls. c, 3×10⁵ bone marrow cells from Col2.3-cre; Cxcl12^fl/fl mice gave significantly lower levels of donor cell reconstitution in the T and B cell lineages but not in the myeloid lineage relative to control bone marrow cells (three experiments with a total of 13–14 recipients per genotype). d, 20 CD150⁺CD48⁻Lineage⁻Sca1⁺cKit⁺ HSCs from Col2.3-cre; Cxcl12^fl/fl mice gave normal donor cell reconstitution (three experiments with a total of 14–15 recipients per genotype), including normal levels of myeloid, B, and T cells (Supplementary Fig. 8c). e–h, Col2.3-cre; Cxcl12^fl/fl bone marrow had normal frequencies of MPPs, CMPs, MEPs, GMPs (e), and committed B lineage progenitors (h) but significantly reduced frequencies of CLPs (f) and IL7Rα⁺LMPPs (g) (n=3–5). i, Col2.3-cre; Cxcl12^fl/fl mice had normal frequencies of myeloerythroid colony-forming progenitors in the bone marrow, spleen, and blood (n=3–6). j, Some Lin⁻IL7Rα⁺ early lymphoid progenitors were adjacent to the endosteum. k–m, Prx1-cre; Cxcl12^fl/fl mice exhibited significant reductions in bone marrow cellularity (k, n=3–4) and the frequencies of HSCs (l), CLPs, and IL7Rα⁺LMPPs (m, n=4–5).Δ, recombined Cxcl12^fl allele; con, control mice. *P<0.05, **P<0.01, ***P<0.001.