Nonablated newborn mouse injection strategy and GFP expression analysis of STAT5ab^–/– C57BL/6 recipient mice. (A) STAT5ab^+/– mice were mated to yield STAT5ab^–/– pups. Because STAT5ab^–/– mice typically survive at much less than a 1:4 ratio, we injected a large number of newborn mice to ensure that STAT5ab^–/– mice would be available for analysis. These newborn pups were injected at 2 to 3 days after birth with adult BM cells harvested from GFP transgenic donor mice. At the time of weaning, mice were genotyped and analyzed by fluorescence-activated cell sorting (FACS) for GFP expression. The bottom of panel A shows the results of representative Western blot for STAT5a expression in brain tissue of wild-type, heterozygote, and STAT5ab^–/– mice. (B) GFP expression in peripheral blood leukocytes of mice of different genotypes is shown for mice analyzed 28 weeks following injection. The GFP expression level was inversely correlated with the expression level of STAT5a in these mice. The number of mice injected in each group is shown below because many circles are overlapping. The genotypes of each group are shown below the graph.