Relative defects in multilineage hematopoietic repopulation by

Pbx1^−/− FL cells. (A) Competitive repopulation assays show thatPbx1^+/−(Ly5.1⁺) FL cells contributed equally with wt (Ly5.2⁺) competitor cells at 18 weeks after transplantation while Pbx1^−/−(Ly5.1⁺) FL cells contributed to fewer than 5% of peripheral blood leukocytes. Data points represent the mean values for 10 recipient animals in each cohort transplanted with FL cells pooled from at least 4 embryos of each genotype. (B) Analysis ofPbx1^+/−and Pbx1^−/−FL cell contribution to myeloid (Gr-1, Mac-1) and lymphoid (B220, CD3) competitive reconstitution at the 18-week time point. (C) Radioprotection assays show the percentage of mice surviving at least 30 days following lethal irradiation. Data are expressed as a function of transplanted cell dose for Pbx1⁺ (pooled wt and Pbx1^+/−) and Pbx1^−/−FL donor cells. Data are from representative experiments replicated at least twice with the use of FL cells pooled from 4 or more embryos of each genotype. (D) Southern blots of genomic DNA from whole BM of wt mice radioprotected by Pbx1⁺ orPbx1^−/−FL cells showing wt and disrupted (knockout [ko]) Pbx1 alleles. Pbx1⁺denotes data pooled from wt and heterozygous cells. The probe consisted of a DNA fragment flanking (3′) and external to the Pbx1targeting construct. The endogenous wt band served as an internal single-copy control signal. The presence of ko allele in BM of mice reconstituted with Pbx1^−/−FL cells indicates that they contributed to long-term reconstitution. Data are shown for 2 representative recipient mice at 3 different concentrations of injected FL cells pooled from at least 4 FLs of each genotype.