Competitive reconstitution assays. (A) Experimental outline of the competition assay between control and mutant FL cells to reconstitute hematopoietic organs of an adult myeloablated recipient on intravenous transplantation. Mutant and wildtype FL cells differ in their Ly5 locus and can be distinguished by FACS analysis using antibodies directed against Ly5.1 (wild-type cells and residual cells from Pep3b recipient) and Ly5.2 (mutant cells). (B) FACS profiles from hematopoietic chimeras for Hoxb4 and Hoxb1-b9 mutants assaying the contribution of mutant (Ly5.2) and wild-type (Ly5.1) cells. (C) Southern blots of BM, spleen (S), or thymus (T) derived from recipients of a mixed Hoxb4^-/- or Hoxb1-9 and wild-type FL transplants. (D) Percentages of mutant and wild-type hematopoietic cells in BM, S, T, and peripheral blood (PB) of mice given transplants with mixed mutant and wild-type FL or BM cells. Each value represents the mean percentage of mutant or wild-type populations measured in 16 different mice. As described in “Materials and methods,” each mutant FL tested for competitive repopulation with wild-type cells was transplanted into 4 recipients and therefore these 16 mice represent 4 mutant FLs. Because not all hematopoietic cells in BM present the leukocyte marker CD45 (Ly5), the sum of Ly5.1 and Ly5.2 cells was assumed to be 100% and the percentages for these populations was recalculated. A color version of this figure is available online as Supplemental Figure S2.