Procedure for generating germline mice carrying the knock-in AML1 allele. (A) Procedure for the targeted insertion (knock-in) of full-length AML1 cDNA or of the Δ446 mutant into wild-type ES cells by homologous recombination. (B) Southern blot analysis of the knock-in allele using XbaI-digested genomic DNA obtained from a representative litter of crossed Δ446-heterozygotes. Lanes 1, 5, and 6: wild-type (+/+). Lanes 4, 7, and 10: homozygote (Δ446/Δ446). Remaining lanes: heterozygote (+/Δ446). (C) Semiquantitative RT-PCR for comparison of the expression of AML1 with that of the HPRT gene in wild-type germline mice (+/+), those homozygous for full-length cDNA (WT/WT), and those homozygous for Δ446 (Δ446/Δ446) genotypes (see “Materials and methods”). Results for 2 independent mice of each genotype are shown. Serially diluted cDNA pools were analyzed. Lanes a, b, and c: 5^–2, 5^–3, and 5^–4 dilutions, respectively. M indicates marker. (D) Peripheral blood cell counts for the mutant mice compared with those for the matched-sibling control mice are indicated by columns. Bars signify standard deviations.