Generation of Flk1⁺/lacZ neo-out mice and Flk1⁺/lacZ del Sw/B neo-out mice lacking the first intronic enhancer. (A) Schematic representation of mutant alleles of Flk1 gene used in this paper. The black box (top row) shows probe for Southern blot analysis. Red boxes show first intronic enhancer located between SwaI and BamHI sites. Arrows show a set of primers for PCR analysis. Characters in bold show restriction enzyme digestion sites. H indicates HindIII; N, NcoI; B, BamHI; S, SmaI; and Sw, SwaI. H in red shows HindIII site introduced by HindIII linker. (B) PCR analysis of Flk1 first intronic sequence. PCR was performed using a set of primers shown in panel A to verify the deletion event between SwaI and BamHI. Lane 1, 10 fg Flk1⁺/lacZ knock-in vector; lane 2, 10 fg Flk1⁺/lacZ del Sw/B knock-in vector; lane 3, DNA extracted from 8.5 dpc wild-type (WT) embryo; lane 4, DNA extracted from 8.5 dpc Flk1⁺/lacZ del Sw/B homozygous embryo.