ROSA26-targeted Flt-1 isoforms rescue flt-1^−/− mutant vessel dysmorphogenesis. Day 8 differentiated ES cultures were stained for PECAM. All transgenic clones partially rescued the vessel dysmorphogenesis of flt-1^−/− vessels (B). Note that targeted sFlt-1 transgene ROSA26 clones (C–F) appear to have more branched vessels than do targeted mFlt-1 transgene ROSA26 clones (G–J). Clone numbers are indicated in the top right of each frame. Bar, 200 μm.