LacZ staining of whole organs from Hprt-Robo4-lacZ mice. (A) Schematic of the wild-type (WT) and ETSmut Hprt-targeted alleles. The 3-kb human ROBO4 promoter with or without the mutation in ETS(1) site, LacZ cDNA and SV40 polyadenylation signal (pA) in the upstream of the Hprt gene are indicated. (B) Organs were harvested from F2 wild-type (WT) or ETSmut Hprt-targeted mice, and processed for whole-mount staining with X-Gal. (C) Sections were prepared from organs of WT or ETSmut mice and stained with X-Gal. A scale bar is indicated in the bottom right panel. (D) Whole-mount E10 embryos (top panel) or day 10 embryoid bodies (bottom panels) from WT and ETSmut Hprt-targeted mice or ES clones were stained with X-Gal, respectively.