WT cells engraft poorly in BMP4-deficient mice after parabiosis. (A) Experimental strategy. (B) Donor cell analysis of the peripheral blood in mutant/WT parabiotic mice and WT/WT parabiotic mice 2 weeks after separation. Significantly fewer circulating WT donor cells are found in the mutant hosts after parabiosis (n = 7), whereas comparable donor engraftment of mutant donor cells into WT hosts (n = 6) or WT donor cells into WT hosts (WT/WT parabionts, n = 3) is observed. *P < .001. (C) BM donor cell engraftment and lineage analysis in 3 pairs of mutant/WT parabionts approximately 10 months after separation. Significantly fewer donor cells are observed in the mutant BM (*P < .006). Total donor cells are shown as a percentage of live cells. Individual lineages are shown as the percentage of donor-derived cells. Error bars show SEM.