Both Smad1 and Smad5 are dispensable for functional fetal liver hematopoiesis. (A) Expression of BMP receptors in WT fetal liver cells analyzed by quantitative RT-PCR. ALK3 is expressed in Lin⁻ Sca-1⁺ AA4.1⁺ fetal liver but is undetectable in LSK CD34⁻ BM cells.^10,22  (B) Representative gel showing screening of Smad5 deletion (PCR) in fetal livers. Only livers with highly deleted Smad1 (data not shown) and Smad5 were used (such as #10). WT littermates lacking Cre have floxed, but undeleted, genes (such as #1). (C) Short-term (ST) donor reconstitution in PB and long-term (LT) contribution in BM. Distribution of myeloid cells (Mac-1), B cells (B220), and T cells (CD3) within the donor population in PB (D) and BM (E) analyzed by FACS long-term after transplantation. Number of myeloid progenitors (F), total cells/femur and primitive LSK cells/femur (G) in BM long-term after transplantation as determined by the number of formed colonies (GM-CFU), differential counts, and FACS, respectively. Data are mean ± SD (n = 5 donors and 15 recipients per genotype). represent WT; , S5^−/−; and ▬, S1/5^−/−.