Inducible Runx1 excision in adult mice induces thrombocytopenia. (A) Schematic representation of Runx1 gene-targeting strategy used to flank exon 4 with LoxP-targeting sites. B indicates BamHI; S, SspI; E4, Runt domain exon 4. (filled boxes) 5′ and 3′ targeting probes. (dashed arrows) BamHI-digested genomic DNA fragments for wild-type (7.3-kb), Floxed (2.8-kb), and excised (2.5-kb) DNA detected with excision (Δ) probe (open boxes) located 3′ to the distal LoxP site. (B) Southern blot analysis of BamHI-digested genomic DNA from bone marrow [B] and spleen [S] cells of representative mice killed at 14, 35, and 91 days after pIpC injection. The dose of pIpC is indicated. The blots are probed with Δ probe, which detects the Floxed (2.8-kb) and excised (2.5-kb) Runx1 alleles. Numbers indicate percentage excision. (C) Mean ± SD of total WBC counts, total red blood cell (RBC) counts, total platelet counts, percentage lymphocytes, and percentage neutrophils in PB of pIpC-treated Runx1^F/F—Tg(Mx1-Cre) (red symbols) and Runx1^F/F (black symbols) mice. Mice were bled 12 days before pIpC injection and 14, 21, 28, 35, 49, 91, 119, and 154 days after pIpC injection. The number of animals evaluated for each genotype at the respective time points is N (Runx1^F/F—Tg(Mx1-Cre) = 14, 14, 12, 8, 10, 9, 8, 7 and 6; N (Runx1^F/F) = 7, 5, 7, 7, 5, 7, 6, 6, and 6.