Whole mount in situ hybridization detects ferrochelatase and luciferase expression in −4.0 TG mouse embryos. Whole-mount in situ hybridization was performed on 15.5 d.p.c. embryos by using antisense DIG-labeled RNA probes. (A) Detection of the luciferase transgene in the fetal liver of luciferase positive (left) and luciferase negative (right) transgenic litter mates. Transversal sections are shown, and the view is from posterior to anterior. (B) and (C) indicate staining in the gonads (left and right arose from different transversal microtome sections) of the luciferase positive mouse shown in (A). (D) Shows the localization of the endogenous murine ferrochelatase gene to the fetal liver at the same developmental stage. In all cases, hybridization to sense RNA probes gave no detectable signal (not shown).