Hematopoietic multipotent progenitors require CXCR4 for multilineage differentiation IL-7 acts as a short-range signal for common lymphoid progenitor differentiation IL-7+ cells are CXCL12-abundant reticular mesenchymal progenitor cells CXCL12 and SCF expressed by IL-7+ cells control the number of HSCs and MPPs in BM