Constitutive Thbd ablation with selective preservation in the placenta in Meox2Cre-Thbd^loxP mice. (A) Thbd-deficient neonates found dead. Arrows indicate hemorrhagic lesions. (B) Photomicrograph of a flash-frozen section prepared from a day 15.5 embryo expressing the Meox2Cre-gene and the mT/mG recombinase reporter gene: red (mT) fluorescence indicates the nonrecombined reporter gene expressed in the placenta, green fluorescence indicates Cre-mediated activation of the mG reporter in the embryo proper, chorionic plate, and fetal blood vessels in the placenta, but lack thereof in all extraembryonic fetal trophoblast cells. (C-D) Immunohistochemical detection of Thbd antigen (brown staining; hematoxylin counterstain) in the day 12 embryo and placenta of Thbd^loxP mice (in panel C, Thbd is detected in the embryo and placenta) and Meox2Cre-Thbd^loxP mice (in panel D, Thbd is present in the placenta, but not the embryo). Scale bars, 1 mm.